The Intermontane Plateaus of the Colorado Plateaus Province, in
the Navaho Section, show young plateaus, stripped structural-platform
or rock terraces, retreating escarpments, mesas, cuestas, shallow canyons,
and dry washes, to San Juan Basin, San Juan Valley, and Chuska
Mountains. In the Dátil Section are found extensive lava flows, and
volcanoes and volcanic necks, such as the Zuñi Mountains, Mount Tay-
lor, and Cabezón Peak.
The Mexican Highland of the Basin and Range Province shows
narrow isolated ranges of largely dissected block mountains separated
by broad silt-deposited desert plains; rock pediments, alluvial fans,
bolsons, playas (dry lake beds), salinas, and dunes. Sandía, Manzano,
San Andrés, Caballos, Magdalena, San Mateo, Black, Mogollón, and
many other ranges are here; also basins such as the Tularosa, Jornada
del Muerto, and Plains of San Agustín; and the Rio Grande, a through-
flowing stream of complex geologic history.
The Sacramento Section includes mature block mountains of gently
tilted strata, block plateaus, and bolsons, such as the Sierra Blanca,
Sacramento, and Guadalupe Mountains, and the Estancia Valley.
The great topographic relief of the State, 10,430 feet (from 2,876
to 13,306), is conditioned by great uplifts and displacements of the
earth's crust. This relief is to a large degree responsible for the great
range of rainfall in the State as well as for the temperatures above and
below zero. There is also a definite connection between the contrast-
ing physiographic relief and the presence in the State of six of the seven
life zones present in North America; the Lower Sonoran, Upper So-
noran, Transition, Canadian, Hudsonian, and Arctic-Alpine, each with
its distinctive assemblage of plants and animals.
The annual rainfall for the whole State ranges from 12 to 16
inches and, although 100 degrees of heat are not infrequent in the sum-
mer, the mean temperature for the year is about 50 degrees.
Few other States possess a more remarkable array of diverse geologic
features or a more complete record of geologic history than New Mex-
ico. There are many breaks in the record; in some instances no strata
were deposited; at other times strata were deposited only to be removed
by subsequent erosion. But it is noteworthy that every period of the
geologic time-table is represented in this State. The most ancient
rocks in New Mexico are possibly 1,000 to 2,000 million years old and
are so exposed in mountain ranges that to see them it is necessary to
ascend rather than to descend, as required in the Grand Canyon of the
Colorado in Arizona.
Throughout much of the Paleozoic era southern New Mexico was