Naturalists tend to ignore State and National borders, preferring to view our planet as a mosaic of geophysical provinces. Most of these regions are large and extend across man's artificial boundaries; the Rocky Mountain Province, for example, stretches through Canada, the U.S. and Mexico.
Another way to view the landscape is through its pattern of watersheds. The largest rivers have watersheds that often cover parts of several geophysical provinces; for example, the Missouri River drains part of the Rocky Mountain, High Plains, Central Lowlands and Ozark Highlands Provinces. By dividing these major watersheds into their secondary components, one gains a better appreciation for the complexity of regional topography; if nothing else, watching for these natural boundaries can make your travels more interesting.
Driving from Colorado to Missouri, today, I crossed only two State lines but passed through a series of watersheds. East of Denver, I-70 remains within the South Platte watershed until it crosses the Palmer Divide, north of Limon. Descending southward through the Big Sandy watershed, a tributary of the Arkansas, the highway then turns to the east and climbs 800 feet onto the High Plains escarpment; there it enters the Republican River watershed, which it occupies all the way to Colby, Kansas. Just beyond Colby, the highway crosses an obscure divide to enter the watershed of the Smoky Hill River; this vast drainage, which also includes the Solomon and Saline Rivers, covers much of central and western Kansas. At Junction City, the Smoky Hill and Republican watersheds merge to become the Kansas River watershed; I-70 occupies this drainage as it crosses the Flint Hills, passes through Topeka and continues on to Kansas City. Finally, the interstate crosses Missouri through the primary watershed of the Missouri River, fording its broad floodplain just west of Columbia.
