The Clayton-Raton Volcanic Field stretches across northeastern New Mexico, extending into southern Colorado and extreme western Oklahoma. Produced by hotspot volcanism that began about 9 million years ago and ended just 40,000 years ago, the axis of the field is oriented NW-SE, extending from the vicinity of Trinidad, Colorado, to Clayton, New Mexico.
Among the many volcanic features that are scattered across the field, the largest is Sierra Grande, a massive shield volcano that rises to an elevation of 8720 feet, nearly 2000 feet above the surrounding High Plains. Shield volcanoes are produced by repeated flows of low-viscosity lava, often yielding a broad, symmetrical cone; Sierra Grande is thought to have formed less than 3 million years ago. Visible throughout northeastern New Mexico, this isolated mountain looms just SSW of Des Moines, where US 64/87 jogs past its northern and eastern flanks.
Though its summit is 4000 feet lower than the crest of the Sangre de Cristo Range, to its west, Sierra Grande's isolation, prominence and massive bulk endow this extinct volcano with a grandeur that range-bound peaks cannot match. I certainly recall my first glimpse of its majestic cone following a long journey across the Great Plains, an awe-inspiring preview of the mountain landscapes that lay ahead.
