San Juan Basin

The San Juan Basin is a large depressed region in northwestern New Mexico bordered on the west by the Defiance Uplift, and the Chuska Mountains, on the north by the San Juan dome, on the south by the Chaco slope and the Zuni Uplift, and on the east by the Naciemento uplift. Cretaceous and Tertiary sedimentary rocks bow down in the San Juan basin into a large, shallow sag approximately 100 miles across.

The sediments that fill the basin were derived from the San Juan Mountains to the north and the southern tip of the Rockies. Both of these mountain ranges were new in Tertiary times and were just beginning to erode. The basin began forming even as the mountains rose and the sediments from that period fill it to a depth of 7000 feet. These strata are easily seen in the canyons cut by drainages to the San Juan River to the north.

The sedimentary rocks that fill this basin contain both source rocks and natural reservoirs for oil and gas, both formed by slow decomposition of plant and animal material within the source rocks. The resevoir rocks of the San Juan basin are Cretaceous and Tertiary sandstones. The San Juan basin gas field is marked by many well sites. The gas is found several thousand feet below the surface, naturally pressurized, eliminating the need for pumping. The gas field extends over a wide area. Well sites in canyons are favored, as the natural erosion has already done some preliminary "drilling" for the wells.

The San Juan Basin was an active seaway connecting the central New Mexico sea with the Paradox Basin in Utah during most of pre-Permian time.

There is a nice set of pages on dinosaurs in New Mexico available from the Albuquerque Museum of Natural History

There is a page on gas and oil resources in the San Juan Basin available from the USGS server.

If, like me, you are confused by the terms used to designate geologic time, a chart, based upon one given in Roadside Geology of Arizona by H. Chronic is available.

In Association with


Navajo Sacred Places, Klara Bonsack Kelley, Harris Francis, Indiana Univ Press.
Native Roads : The Complete Motoring Guide to the Navajo and Hopi Nations,
Fran Kosik, George Hardeen, Creative Solutions Pub.
Named in Stone and Sky : An Arizona Anthology, Gregory McNamee (Editor),
Univ of Arizona Press.
Burntwater, Scott Thybony, Univ of Arizona Press.
Talking to the Ground : One Family's Journey on Horseback Across the Sacred Land of the Navajo
Douglas Preston, Univ of New Mexico Press.
A Guide Book to Highway 66, Jack D. Rittenhouse, Univ of New Mexico Press.
Basin and Range, John McPhee, Noonday Press.
Navajo Country : A Geology and Natural History of the Four Corners Region, Donald Baars, Univ. New Mexico Press.
The Colorado Plateau : A Geologic History, Donald L. Baars, Univ of New Mexico Press.
Roadside Geology of New Mexico, Halka Chronic, Mountain Press.

In Association with
In Association with

© 1994 Karen M. Strom

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