Baby Rocks is an excellent roadside tutorial on the effects of differential weathering
on rocks of the San Rafael Group. The San Rafael Group is a middle aged formation of
sedimentary rock formed in the Mesozoic ("Middle Aged" Era), composed of sandstone,
siltstone and claystone. The sandstone and siltstone are thick, dark red rocks which
suggest deposition in floodplains. In some places, the rock seems to have been eroded
followed by more deposition. This too suggests a floodplain origin.
Baby Rocks shows these layers broken by many vertical joints and small faults, allowing water
to enter and further the erosion. The rock beds at the base of this outcropping sometimes
show oddly distorted layers. These deformations occur when sliding and slumping take place
before the rock has hardened.
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.
Roadside Geology of New Mexico, Halka Chronic, Mountain 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.
- 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 Arizona, Halka Chronic, Mountain Press.
© 1994-99 Karen M. Strom
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