As the Mesozoic Era ended, 65 million years ago, the dinosaurs were dying out and the Rocky Mountains were crumpling skyward. In concert with their rise, the forces of erosion began to work on these highlands and aprons of debris, carried by wind and water, spread out from their flanks. Throughout much of the Tertiary Period, the mountain summits barely poked above these vast plains of debris.
Then, in the Miocene Epoch (some 20 million years ago) a second, more general uplift of the Mountain West began, adding 5000 feet to elevations across the Colorado Plateau and Rocky Mountain Province. This uplift, which continued into the Pliocene, accelerated stream erosion throughout the region; the process was further enhanced by the cold, wet climate of the Pleistocene, as mountain glaciers carved deep canyons and massive amounts of meltwater carried away much of the erosional debris that had enveloped the mountains.
When early explorers and settlers reached western North America, the Front Range of the Rockies imposed a formidable barrier from Canada to New Mexico. Though steep, narrow passes were adequate for travel by foot or horseback, the search for a train route uncovered an area in southern Wyoming where Tertiary sediments had survived the elements of erosion. Known to geologists as The Gangplank, this wide, natural pass west of Cheyenne offers a gradual climb between the watersheds of the North and South Platte Rivers; the Union Pacific line and Interstate 80 use this route today, crossing the Laramie Range between the High Plains and the Laramie Basin.
Sunday, December 21, 2008
Saturday, December 20, 2008
Bird Count
More than most people, I enjoy solitude, especially when visiting wild areas. The sights, sounds and smells of nature are, in my opinion, best appreciated in the absence of human conversation. But twice each year, near Christmas and in the spring, I take part in the annual Audubon birding counts, established to monitor the status of regional bird populations.
Our group is assigned to rolling farmlands south of Columbia, between the Missouri River, on the west, and U.S. 63. We gathered just before dawn and set out to survey are region, winding along country roads and stopping at selected sites to look for birds. It was a cold, gray day but the birding was decent and most expected species were found; as usual, juncos, crows, robins, blue jays, cardinals, flickers and starlings were among the more common. We also saw red-tailed and red-shouldered hawks, a lone bald eagle, a variety of woodpeckers, yellow-rumped warblers, purple finches, swamp sparrows and northern mockingbirds; during our six hour excursion, forty species were tallied.
The highlight of today's count was the large number of cedar waxings. In most years, we see several flocks of these attractive birds, generally yielding a total of fifty or so. Today, we saw hundreds of waxwings; in fact, it was the most numerous bird on the list, even surpassing our tallies for juncos and starlings. Though the reason is uncertain, it is likely that these nomadic birds abandoned more northern parts of their range after recent heavy snows across that region.
Our group is assigned to rolling farmlands south of Columbia, between the Missouri River, on the west, and U.S. 63. We gathered just before dawn and set out to survey are region, winding along country roads and stopping at selected sites to look for birds. It was a cold, gray day but the birding was decent and most expected species were found; as usual, juncos, crows, robins, blue jays, cardinals, flickers and starlings were among the more common. We also saw red-tailed and red-shouldered hawks, a lone bald eagle, a variety of woodpeckers, yellow-rumped warblers, purple finches, swamp sparrows and northern mockingbirds; during our six hour excursion, forty species were tallied.
The highlight of today's count was the large number of cedar waxings. In most years, we see several flocks of these attractive birds, generally yielding a total of fifty or so. Today, we saw hundreds of waxwings; in fact, it was the most numerous bird on the list, even surpassing our tallies for juncos and starlings. Though the reason is uncertain, it is likely that these nomadic birds abandoned more northern parts of their range after recent heavy snows across that region.
Friday, December 19, 2008
The Tahoe Basin
Though the Sierra Batholith formed back in the Mesozoic Era, this massive pluton of rock did not rise to create the Sierra-Nevada Range until the late Tertiary Period, about 3-4 million years ago. As it rose, the forces of erosion began to sculpt its summits and fault lines developed along its margins. Along the northeast edge of the batholith, a block of crust (known as a graben) dropped between parallel faults, with the Sierra rising to its west and the Carson Range uplifted to its east; the resulting basin is now known as Tahoe.
Streams from the surrounding highlands gradually filled the basin, the margin of which was continually molded by uplift, faulting, landslides, volcanic debris and glacial erosion; the latter was especially significant during the Pleistocene Epoch as glacial valleys formed along the west edge of the basin, glacial moraines altered drainage patterns and glacial meltwater added significant depth to the basin's lake. As one might expect, the surface level of Lake Tahoe, which now sits at 6225 feet, rose and fell significantly over the past 2 million years.
Today, the Truckee River is the only outlet from Lake Tahoe, flowing northeastward into the Great Basin, where it feeds Pyramid Lake. Lake Tahoe itself, with a maximum depth of 1645 feet and a surface area of 191 square miles, is the largest alpine lake in North America and the third deepest lake on the Continent (behind Great Slave Lake and Crater Lake). Known for its scenic setting and for the clarity of its water, Lake Tahoe sits above two fault lines, making the area prone to earthquakes and a potential tsunami; like all lakes, mountains, plains and canyons, it is a beautiful but temporary feature of our planet's landscape!
Streams from the surrounding highlands gradually filled the basin, the margin of which was continually molded by uplift, faulting, landslides, volcanic debris and glacial erosion; the latter was especially significant during the Pleistocene Epoch as glacial valleys formed along the west edge of the basin, glacial moraines altered drainage patterns and glacial meltwater added significant depth to the basin's lake. As one might expect, the surface level of Lake Tahoe, which now sits at 6225 feet, rose and fell significantly over the past 2 million years.
Today, the Truckee River is the only outlet from Lake Tahoe, flowing northeastward into the Great Basin, where it feeds Pyramid Lake. Lake Tahoe itself, with a maximum depth of 1645 feet and a surface area of 191 square miles, is the largest alpine lake in North America and the third deepest lake on the Continent (behind Great Slave Lake and Crater Lake). Known for its scenic setting and for the clarity of its water, Lake Tahoe sits above two fault lines, making the area prone to earthquakes and a potential tsunami; like all lakes, mountains, plains and canyons, it is a beautiful but temporary feature of our planet's landscape!
Center of the Storm
This week's powerful winter storm, on its way from Southern California to New England, passed just north of Columbia through the night. As it approached, energized by the jet stream, a thunderstorm erupted above the city, a startling event after days of frigid weather. Strong, counterclockwise winds, surrounding the central low pressure, brought in warm air from the south and, at dawn, it is 42 degrees F; winds are from the southwest, gusting to 40 mph.
As the storm continues its journey to the northeast, its trailing cold front will sweep across Missouri, the winds will shift to the west-northwest and the temperature will fall through the day. We can expect relatively mild conditions over the next 36 hours before another Arctic air mass plunges into the Heartland. Just another winter in the Midwest!
As the storm continues its journey to the northeast, its trailing cold front will sweep across Missouri, the winds will shift to the west-northwest and the temperature will fall through the day. We can expect relatively mild conditions over the next 36 hours before another Arctic air mass plunges into the Heartland. Just another winter in the Midwest!
Thursday, December 18, 2008
Transcontinental Express
Developing at the base of a deep, western trough, the latest winter storm brought heavy snows to the Southern California Mountains, southern Nevada desert and Mogollon Rim yesterday. This morning, the storm is moving toward the Four Corners, spreading snow across the Colorado Plateau and Southern Rockies.
By this afternoon, the storm will hitch a ride on the jet stream and move across the Central Plains. Rain, sleet and freezing rain will develop along its path (Kansas-Missouri-Illinois) and heavy snow is forecast for the Upper Midwest. Moving on through the night, this weather system will be in New England by tomorrow morning, ensuring a White Christmas for much of that region.
Of course, most North American storm systems move from west to east, governed by the prevailing winds. The speed of their movement is generally related to their proximity to the jet stream and this one is taking the Transcontinental Express!
By this afternoon, the storm will hitch a ride on the jet stream and move across the Central Plains. Rain, sleet and freezing rain will develop along its path (Kansas-Missouri-Illinois) and heavy snow is forecast for the Upper Midwest. Moving on through the night, this weather system will be in New England by tomorrow morning, ensuring a White Christmas for much of that region.
Of course, most North American storm systems move from west to east, governed by the prevailing winds. The speed of their movement is generally related to their proximity to the jet stream and this one is taking the Transcontinental Express!
Wednesday, December 17, 2008
Owl Nights
We are now facing the long, cold nights of winter, the season of the owl. Equipped with superb vision and hearing and insulated with a dense coat of feathers, the owls rule these frigid nights, oblivious to the conditions. Their prey, primarily mice, voles and cottontails, must stay active to survive and the patient owls are waiting.
This is, in fact, the onset of the breeding season for great horned owls and their hoots will build over the next six weeks. We humans, not naturally designed for this season, retreat to our heated dens; a night in the cold and snow is but a bad dream. But we take solace in the call of the owl, a message that nature's cycle endures and that, in time, spring will arrive.
This is, in fact, the onset of the breeding season for great horned owls and their hoots will build over the next six weeks. We humans, not naturally designed for this season, retreat to our heated dens; a night in the cold and snow is but a bad dream. But we take solace in the call of the owl, a message that nature's cycle endures and that, in time, spring will arrive.
Monday, December 15, 2008
A Taste of the Arctic
Those of us who live in the Temperate and Tropical Zones cannot truly appreciate the conditions faced by humans and other animals that inhabit the polar regions. This latest Arctic outbreak, triggered by a broad dip in the jet stream, is giving us a taste of life at the Poles. Extreme cold has invaded the Northern Plains, where morning lows hovered at 20-30 degrees F below zero; add in the wind effect and we're talking serious cold!
The development of extreme cold requires a lack of solar heating and limited cloud cover; the latter permits heat to radiate into space and is a common feature of the dry polar climate. In the Arctic, a perpetual night began in mid November and will last until late January; the only warming that they will experience is via southerly winds ahead of polar fronts. In a twist of fate, their relief is at our expense as the intense, Arctic cold is displaced to the south; on the positive side, this polar air is extremely dry and precipitation, in the form of rain, snow or ice, is generally short-lived, moving off with the frontal boundary as the cold, dense air rushes to the south and east.
Looking out from my office window this morning, I watched a snowball moon set behind a flat shelf of snow-white clouds. The temperature was 6 degrees F.
The development of extreme cold requires a lack of solar heating and limited cloud cover; the latter permits heat to radiate into space and is a common feature of the dry polar climate. In the Arctic, a perpetual night began in mid November and will last until late January; the only warming that they will experience is via southerly winds ahead of polar fronts. In a twist of fate, their relief is at our expense as the intense, Arctic cold is displaced to the south; on the positive side, this polar air is extremely dry and precipitation, in the form of rain, snow or ice, is generally short-lived, moving off with the frontal boundary as the cold, dense air rushes to the south and east.
Looking out from my office window this morning, I watched a snowball moon set behind a flat shelf of snow-white clouds. The temperature was 6 degrees F.
Sunday, December 14, 2008
Windblown Ducks
It was a gray, mild, windy afternoon at Eagle Bluffs yesterday, as a strong southerly flow developed in advance of the next cold front. As usual, there was a large number of wintering ducks at this Missouri floodplain conservation area, southwest of Columbia. Mallards, pintails, gadwalls and green-winged teal were well represented and ring-necked ducks were especially abundant. On the other hand, only a small number of Canada geese were seen and no snows graced the refuge.
The highlight of this visit was the aerial spectacle of the numerous ducks as they attempted to move among the lakes, ponds and sloughs, challenged by the strong southerly winds. Those flying with the wind zoomed effortlessly across the landscape while other flocks, heading against the gale, were blown about, forcing them to veer off course or drop to the surface and wait for the wind to diminish. Many, especially the flight-challenged coots, huddled along the leeward edge of cattails while diving ducks, comfortable in the choppy water, formed rafts on the larger lakes.
To one who looked out across the refuge, the restless ducks, moving in small groups or large flocks, at various angles to the persistent wind, had the appearance of windblown leaves, scattered through the winter sky. Even they, equipped with lean, muscular bodies and instinctual flight skills, were at the mercy of nature's power.
The highlight of this visit was the aerial spectacle of the numerous ducks as they attempted to move among the lakes, ponds and sloughs, challenged by the strong southerly winds. Those flying with the wind zoomed effortlessly across the landscape while other flocks, heading against the gale, were blown about, forcing them to veer off course or drop to the surface and wait for the wind to diminish. Many, especially the flight-challenged coots, huddled along the leeward edge of cattails while diving ducks, comfortable in the choppy water, formed rafts on the larger lakes.
To one who looked out across the refuge, the restless ducks, moving in small groups or large flocks, at various angles to the persistent wind, had the appearance of windblown leaves, scattered through the winter sky. Even they, equipped with lean, muscular bodies and instinctual flight skills, were at the mercy of nature's power.
Saturday, December 13, 2008
New England Orogenies
New England has a complex geologic history and, like much of the western U.S., was pieced together by a series of exotic terrains. At the beginning of the Ordovician Period, the east coast of the region was west of what is now the Hudson Valley; then, about 450 million years ago (MYA), an elongated island chain collided with the Northeast coast, adding much of western New England and a large portion of the Canadian Maritime Provinces. This collision initiated the Taconic Orogeny, uplifting a range of mountains from northeast Canada to present-day Virginia.
Fifty million years later, the Avalon Subcontinent, which sat in the northern Iaepetus Ocean, between the North American and European Continents, slammed into New England, adding coastal New England, Nova Scotia and the Avalon Peninsula of Newfoundland; its northeast segment would become northern France and the British Isles. The collision of Avalon with North America triggered the Acadian Orogeny, raising mountains where the Northern Appalachians now stand.
By the end of the Devonian Period, some 350 MYA, these ancestral ranges had nearly eroded to the surface but a new, more extensive Orogeny would soon take place. Throughout the Carboniferous Period, the age of extensive fern forests, giant amphibians and primitive reptiles, the Iaepetus Ocean continued to close, drawing Africa and North America together. The eventual collision of these Continents (320-250 MYA) would produce the Appalachian Orogeny, lifting a continuous chain of mountains from eastern Canada to eastern Oklahoma; these are now known as the Appalachian Mountains (from New England to Alabama) and the Ouachitas (west of the Mississippi Valley). Initially resembling the modern Rockies and Alps, these older mountains have since eroded into lower summits which, except in northern New England, are rounded off and covered by forest.
Fifty million years later, the Avalon Subcontinent, which sat in the northern Iaepetus Ocean, between the North American and European Continents, slammed into New England, adding coastal New England, Nova Scotia and the Avalon Peninsula of Newfoundland; its northeast segment would become northern France and the British Isles. The collision of Avalon with North America triggered the Acadian Orogeny, raising mountains where the Northern Appalachians now stand.
By the end of the Devonian Period, some 350 MYA, these ancestral ranges had nearly eroded to the surface but a new, more extensive Orogeny would soon take place. Throughout the Carboniferous Period, the age of extensive fern forests, giant amphibians and primitive reptiles, the Iaepetus Ocean continued to close, drawing Africa and North America together. The eventual collision of these Continents (320-250 MYA) would produce the Appalachian Orogeny, lifting a continuous chain of mountains from eastern Canada to eastern Oklahoma; these are now known as the Appalachian Mountains (from New England to Alabama) and the Ouachitas (west of the Mississippi Valley). Initially resembling the modern Rockies and Alps, these older mountains have since eroded into lower summits which, except in northern New England, are rounded off and covered by forest.
Thursday, December 11, 2008
Bayou Snow and Northeast Ice
The latest polar plunge, triggered by a dip in the jet stream, was deeper than initially forecast, allowing frigid air to reach the Gulf Coast. At the same time, this advance was rapid and broad, shoving the southern storm eastward rather than northeastward.
Sitting over Mississippi this morning, the powerful storm is raking the Southeast with heavy rains and its "wrap-around" moisture, forced to rise above the entrenched cold, is producing light snow across east Texas and much of Louisiana. The east edge of the polar trough now stretches along the Appalachians and, as the storm moves up the Atlantic Coast, inland snows and coastal rains will be separated by a swath of ice.
Once again, the exact location and extent of the ice storm is difficult to predict but current forecasts suggest crippling conditions will develop from northern Virginia to southern New England. Meteorology is certainly one of the most interesting and frustrating fields of natural science!
Sitting over Mississippi this morning, the powerful storm is raking the Southeast with heavy rains and its "wrap-around" moisture, forced to rise above the entrenched cold, is producing light snow across east Texas and much of Louisiana. The east edge of the polar trough now stretches along the Appalachians and, as the storm moves up the Atlantic Coast, inland snows and coastal rains will be separated by a swath of ice.
Once again, the exact location and extent of the ice storm is difficult to predict but current forecasts suggest crippling conditions will develop from northern Virginia to southern New England. Meteorology is certainly one of the most interesting and frustrating fields of natural science!
Tuesday, December 9, 2008
Dueling Rams
Rocky Mountain bighorn sheep, one of four wild sheep species in western North America, inhabit the Central and Southern Rockies, from Alberta to New Mexico. Grazers, they feed on grasses and forbs, favoring steep, sunny slopes; ewes and their young tend to remain at lower elevations of the foothills and mountains while bachelor herds may be found above timberline during the summer months.
Their annual rut, featuring head-on collisions of the 400-pound rams, peaks in December and is best witnessed in foothill canyons, below 9000 feet. These duels determine breeding rights and, after this seasonal frenzy, all spend the winter in peaceful coexistence. Impregnated females give birth to a single lamb (twins are rare) in late May or June, by which time the rambunctious males have moved to higher ground. The lifespan of the Rocky Mountain bighorn averages 10-12 years but their gregarious lifestyle makes them susceptible to outbreaks of parasitic disease, especially lungworm pneumonia; others die from falls or from predation by humans, mountain lions or coyotes.
There are many places to observe the bighorn rut throughout Colorado; some of the more reliable locations along the Front Range include Waterton Canyon (southwest of Denver), Mueller State Park (west of Colorado Springs), along I-70 (across from Georgetown) and Big Thompson Canyon (U.S.34, west of Loveland). Regardless of where you go, bring warm, layered clothing and binoculars; be aware that dogs are not permitted in Waterton Canyon.
Their annual rut, featuring head-on collisions of the 400-pound rams, peaks in December and is best witnessed in foothill canyons, below 9000 feet. These duels determine breeding rights and, after this seasonal frenzy, all spend the winter in peaceful coexistence. Impregnated females give birth to a single lamb (twins are rare) in late May or June, by which time the rambunctious males have moved to higher ground. The lifespan of the Rocky Mountain bighorn averages 10-12 years but their gregarious lifestyle makes them susceptible to outbreaks of parasitic disease, especially lungworm pneumonia; others die from falls or from predation by humans, mountain lions or coyotes.
There are many places to observe the bighorn rut throughout Colorado; some of the more reliable locations along the Front Range include Waterton Canyon (southwest of Denver), Mueller State Park (west of Colorado Springs), along I-70 (across from Georgetown) and Big Thompson Canyon (U.S.34, west of Loveland). Regardless of where you go, bring warm, layered clothing and binoculars; be aware that dogs are not permitted in Waterton Canyon.
Monday, December 8, 2008
Southern Storm
A storm has developed over the Southern Plains, just ahead of the next polar plunge. As the cold front pushes to the east-southeast, this storm will move northeastward, pulling in plenty of moisture from the Gulf of Mexico.
Rain will develop ahead of the front while heavy snow is forecast for the Upper Midwest. The exact position of the rain-snow line will depend upon the relative positions of the storm and the front; such uncertainty is a challenge and a potential source of embarrassment for meteorologists. Here in Missouri, we are beginning to feel the southerly flow this morning, with a dawn temperature near 40 degrees F; we should remain on the warm side of the system for the brunt of the storm and significant rainfall is forecast for tonight and tomorrow.
The primary benefit of this storm will likely be seen across the Southeast, where a few days of rain should bring some relief from the prolonged drought. Those on the snowy side of the front may not share their appreciation!
Rain will develop ahead of the front while heavy snow is forecast for the Upper Midwest. The exact position of the rain-snow line will depend upon the relative positions of the storm and the front; such uncertainty is a challenge and a potential source of embarrassment for meteorologists. Here in Missouri, we are beginning to feel the southerly flow this morning, with a dawn temperature near 40 degrees F; we should remain on the warm side of the system for the brunt of the storm and significant rainfall is forecast for tonight and tomorrow.
The primary benefit of this storm will likely be seen across the Southeast, where a few days of rain should bring some relief from the prolonged drought. Those on the snowy side of the front may not share their appreciation!
Sunday, December 7, 2008
Sunday Driver
When I was a boy, my father used to get angry with "Sunday drivers," those people who drove along in a leisurely fashion, taking in the sights. Now, in middle age, I am one of them.
Today's drive took me southwest of Columbia, looping among farms, across the Missouri River floodplain and past the outer sprawl of this college town. The bright sky, cold and blue, was in stark contrast to the faded greens and browns of the early winter landscape. The usual mix of rural birds, dominated by red-tailed hawks, American kestrels and mourning doves, perched along the roadways and placid farm animals, well fed and content, reflected the serenity of country life. Hoping to spot a flock of snow geese heading south, I saw only an occasional group of Canadas, honking their way above the farmlands.
In truth, it's not easy to take a leisurely drive through the country anymore; drop below forty and you'll soon have a pickup on your bumper. Humans continue to fill the open spaces and the pace of life has increased in concert. The Sunday driver is a threatened species!
Today's drive took me southwest of Columbia, looping among farms, across the Missouri River floodplain and past the outer sprawl of this college town. The bright sky, cold and blue, was in stark contrast to the faded greens and browns of the early winter landscape. The usual mix of rural birds, dominated by red-tailed hawks, American kestrels and mourning doves, perched along the roadways and placid farm animals, well fed and content, reflected the serenity of country life. Hoping to spot a flock of snow geese heading south, I saw only an occasional group of Canadas, honking their way above the farmlands.
In truth, it's not easy to take a leisurely drive through the country anymore; drop below forty and you'll soon have a pickup on your bumper. Humans continue to fill the open spaces and the pace of life has increased in concert. The Sunday driver is a threatened species!
Saturday, December 6, 2008
California's Great Valley
Looking at a map of the U.S., one might think that California's Central Valley, on the west coast, and the Chesapeake Bay, on the east, were formed in a similar way; but they would be wrong. While the Chesapeake represents a drowned river valley, the Great Valley of the Golden State is far more complex.
When the Atlantic Ocean began to open, during the Jurassic Period, the west coast of the North American Plate was forced to collide with the Farallon Plate, which underlied what is now the eastern Pacific Ocean; at that time, the west coast of North America was at the longitude of central Utah. As pressure mounted, the Farallon Plate was forced to subduct beneath North America and, as the latter moved westward, a series of exotic terrains and volcanic island arcs were added to the Continent. Between these land masses, seaways were forced to close and, in the process, their oceanic crust was either subducted beneath the growing continent or forced to crumple onto its edge.
The area now covered by California's Great Valley was once one of these entrapped seaways. In fact, it was a deep subduction canyon; to its east, the Farallon plate was melting into the massive batholith of the Sierra Nevada. Over time, this seaway became surrounded by mountainous terrain as the Cascades, Sierra, Coastal Range and Transverse Range formed; sea deposits, volcanic debris and erosional sediments from these highlands gradually filled the sea basin and the surface of the inland sea rose and fell in concert with changes in the Earth's climate. Its connection with the Pacific, once at the latitude of Monterey, shifted northward as the Farallon subduction ended and land shifts along the San Andreas Fault began to reshape the coast.
Eventually filled to the brim with sediments, the massive estuary shrunk to its famous remnant: San Francisco Bay. Throughout the Pleistocene, extensive meltwater lakes covered most of the Valley but, today, reservoirs and water diversion have cut off most of that flow, threatening the health of the Bay and its adjacent wetlands. The Valley itself, once a seaway, has become a flat landscape of desert, irrigated croplands and cities; beneath its surface are miles of sediment.
When the Atlantic Ocean began to open, during the Jurassic Period, the west coast of the North American Plate was forced to collide with the Farallon Plate, which underlied what is now the eastern Pacific Ocean; at that time, the west coast of North America was at the longitude of central Utah. As pressure mounted, the Farallon Plate was forced to subduct beneath North America and, as the latter moved westward, a series of exotic terrains and volcanic island arcs were added to the Continent. Between these land masses, seaways were forced to close and, in the process, their oceanic crust was either subducted beneath the growing continent or forced to crumple onto its edge.
The area now covered by California's Great Valley was once one of these entrapped seaways. In fact, it was a deep subduction canyon; to its east, the Farallon plate was melting into the massive batholith of the Sierra Nevada. Over time, this seaway became surrounded by mountainous terrain as the Cascades, Sierra, Coastal Range and Transverse Range formed; sea deposits, volcanic debris and erosional sediments from these highlands gradually filled the sea basin and the surface of the inland sea rose and fell in concert with changes in the Earth's climate. Its connection with the Pacific, once at the latitude of Monterey, shifted northward as the Farallon subduction ended and land shifts along the San Andreas Fault began to reshape the coast.
Eventually filled to the brim with sediments, the massive estuary shrunk to its famous remnant: San Francisco Bay. Throughout the Pleistocene, extensive meltwater lakes covered most of the Valley but, today, reservoirs and water diversion have cut off most of that flow, threatening the health of the Bay and its adjacent wetlands. The Valley itself, once a seaway, has become a flat landscape of desert, irrigated croplands and cities; beneath its surface are miles of sediment.
Friday, December 5, 2008
The Winter Hawk
Having bred and summered across northern Canada and Alaska, rough-legged hawks drift southward through autumn and winter in the U.S.; since they favor open country, these large buteos are best observed across the Great Plains and Intermountain West.
Heavy bodied and long-winged, rough-legged hawks are identified by their appearance and their behavior. Field marks include a light-colored head, dark patches at the bend of each wing and a white tail with a black terminal band; their name reflects prominent feathering of their legs and feet. Despite their size, these raptors often hunt by hovering over their prey and are known for their habit of perching precariously on thin snags or limbs.
Rough-legs feed primarily on lemmings, mice and voles but may feast on the remains of deer or pronghorns that succumb to the winter snows. Come spring, they return to their Arctic and Subarctic haunts where they nest on cliffs or rocky outcrops.
Heavy bodied and long-winged, rough-legged hawks are identified by their appearance and their behavior. Field marks include a light-colored head, dark patches at the bend of each wing and a white tail with a black terminal band; their name reflects prominent feathering of their legs and feet. Despite their size, these raptors often hunt by hovering over their prey and are known for their habit of perching precariously on thin snags or limbs.
Rough-legs feed primarily on lemmings, mice and voles but may feast on the remains of deer or pronghorns that succumb to the winter snows. Come spring, they return to their Arctic and Subarctic haunts where they nest on cliffs or rocky outcrops.
Thursday, December 4, 2008
Colds and the Cold
As the first major blast of winter envelops much of the country, children and adults will be cautioned to avoid "catching cold." After all, the flu and common cold are widespread at this time of year and many assume that cold weather is responsible.
In a way, it is responsible, keeping more people indoors and close together. All of our common viruses are acquired from other persons, either through intimate contact or via droplets spread by sneezing and coughing. The more interaction we have with others, the more likely we are to become infected.
But while prolonged exposure without proper clothing can be harmful (or even fatal), there is little evidence that cold air, itself, increases our risk for infections. Rather, if properly attired, outdoor exercise is just as beneficial in winter as it is during any other season. And beyond its aerobic and stress-reducing benefits, the winter walk takes you away from the viral reservoirs in our homes, offices and shopping malls!
In a way, it is responsible, keeping more people indoors and close together. All of our common viruses are acquired from other persons, either through intimate contact or via droplets spread by sneezing and coughing. The more interaction we have with others, the more likely we are to become infected.
But while prolonged exposure without proper clothing can be harmful (or even fatal), there is little evidence that cold air, itself, increases our risk for infections. Rather, if properly attired, outdoor exercise is just as beneficial in winter as it is during any other season. And beyond its aerobic and stress-reducing benefits, the winter walk takes you away from the viral reservoirs in our homes, offices and shopping malls!
Tuesday, December 2, 2008
The Eastern Quail
Represented by more than 20 subspecies, the northern bobwhite inhabits central and eastern North America, from southern Canada to Mexico; introduced populations are also found in the Pacific Northwest. Despite their broad range, these small quail are subject to periodic die-offs related to severe cold or heavy snow and are threatened by habitat loss in many areas.
Northern bobwhites favor brushlands and immature woodlands where they forage for insects, seeds and berries. Once maintained by occasional wildfires, drought and storms, such habitat has been replaced by suburban sprawl, crop fields, tree farms and mature forest across much of the quail's range. Bobwhites pair off intermittently throughout the spring and summer, raising several broods each year; however, this high reproductive rate is balanced by loss due to weather or predation (fox, weasels, accipiters, owls) and most chicks die within a year. By October, survivors gather in coveys of 20-30 birds, moving and feeding as a group before huddling together on cold winter nights.
As I learned during my boyhood in southern Ohio, bobwhites are more often heard than seen throughout the warmer months, when the distinctive call of the male echoes across fields and farmlands. During the fall and winter, these quail are usually encountered when hikers or dogs spook a covey, causing the members to explode from the brush in all directions.
Northern bobwhites favor brushlands and immature woodlands where they forage for insects, seeds and berries. Once maintained by occasional wildfires, drought and storms, such habitat has been replaced by suburban sprawl, crop fields, tree farms and mature forest across much of the quail's range. Bobwhites pair off intermittently throughout the spring and summer, raising several broods each year; however, this high reproductive rate is balanced by loss due to weather or predation (fox, weasels, accipiters, owls) and most chicks die within a year. By October, survivors gather in coveys of 20-30 birds, moving and feeding as a group before huddling together on cold winter nights.
As I learned during my boyhood in southern Ohio, bobwhites are more often heard than seen throughout the warmer months, when the distinctive call of the male echoes across fields and farmlands. During the fall and winter, these quail are usually encountered when hikers or dogs spook a covey, causing the members to explode from the brush in all directions.
Monday, December 1, 2008
Winter Arrives
While the winter solstice is still three weeks away, the calendar has flipped to December and the last 24 hours have provided the first real taste of winter. Though periods of cold weather were spaced through the autumn and warm interludes are sure to follow, the cold, darkness, wind and snow of this past day surely marked a transition.
Cold temperatures, day and night, will now rule until March, when the sun begins to reclaim its territory. In the meantime, darkness and quiet will prevail, a survival mode will be adopted and hunters will rule the landscape. And, of course, many humans will retreat to the great indoors and dream of spring.
But those of us who relish the stark beauty of winter will take to the deserted trails and enjoy the quiet solitude of this maligned season. There we will find that our wild neighbors, undaunted by the cold, have no interest in the calendar. For them, retreat is not an option.
Cold temperatures, day and night, will now rule until March, when the sun begins to reclaim its territory. In the meantime, darkness and quiet will prevail, a survival mode will be adopted and hunters will rule the landscape. And, of course, many humans will retreat to the great indoors and dream of spring.
But those of us who relish the stark beauty of winter will take to the deserted trails and enjoy the quiet solitude of this maligned season. There we will find that our wild neighbors, undaunted by the cold, have no interest in the calendar. For them, retreat is not an option.
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