NOTE ON THE RED BEDS OF THE RIO GRANDE REGION 
IN CENTRAL NEW MEXICO: 
WILLIS T. LEE 
During the summers of 1904 and 1905 the writer was engaged in 
geologic investigations in the Rio Grande valley in central New 
Mexico. The results will be set forth in detail in the near future, 
but a preliminary statement is here given of certain facts which 
throw some light on the complex problems of the Red beds. 
There are exceptional opportunities for geologic observations in 
the Rio Grande valley. The region is one in which many monoclinal 
or block mountains occur, having precipitous, scarp-like faces in 
which the various geologic formations, ranging in age from pre- 
Cambrian to Quaternary, are conspicuously exposed. The Red 
beds here described outcrop at the surface with minor interruptions 
from Galisteo Creek at the southern end of the Rocky Mountains, 
southward to Rincon, a distance of about 200 miles. They were 
examined with care in many places east of the Rio Grande, notably 
in Galisteo canyon; at the northern end of Sandia mountains; in 
Abo canyon east of Belen; in the mountains east of Socorro; in 
San Andreas mountains east of Engle; and in the Caballos-Fra 
Cristobal range north of Rincon. 
Throughout this distance the Red beds are uniform in character, 
consisting usually of three more or less distinct divisions. The lowest 
division is composed principally of massive, dark red sandstone, with 
a maximum observed thickness of about 800 feet. The middle 
division consists of pink and white shale and gypsum, with a sub- 
ordinate amount of limestone. ‘The limestone is not always present, 
and the gypsum varies in thickness. In some places, as in Galisteo 
canyon at the northern end of the region, the massive gypsum is 
about 140 feet thick, with the accompanying shale inconspicuous 
and the limestone practically absent. In other places the gypsum 
is distributed in thin beds through a considerable thickness of shale 
t Published by permission of the Director of the U. S. Geological Survey. 
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