Perra and Lerma), but it also contained sequential botan- 
ical remains, some of which are relevant to the problem 
of the early use and evolutionary development of maize. 
As an introduction to the study of the specimens of maize 
from this site, consideration of the location, geography, 
excavation, stratigraphy and cultural sequences of the 
La Perra Cave is here presented. 
This rock shelter was discovered on a brief survey of 
the Canyon Diablo in March 1949, under the guidance 
of Pedro Lerma of Los Angeles, Tamaulipas. It is about 
18 miles northeast of the town of Los Angeles, about 
one-quarter mile north of the point where La Perra Can- 
yonenters the Canyon Diablo. The cave is on the steep 
west side of the valley. It is situated more than 150 feet 
above the arroyo bed in the middle of a vine and shrub- 
covered, 100-foot-high cliff, at a point about 60 feet above 
the base. At the foot of the cliff is a talus slope covered 
with dense vegetation. The cave is not readily accessible, 
but can be approached by ascending a stream bed 400 
feet north of it until a ledge at the level of the cave is 
reached. From here, one proceeds, preferably on hands 
and knees, southward along this ledge to the shelter. It 
is also possible to come down to the cavern from the 
plateau above, but, unfortunately, this approach was not 
discovered until after the excavations were completed. 
The cave itself is situated in thinly-bedded Cretaceous 
limestone. It is about 23 feet deep, 40 feet wide at the 
mouth, 48 feet wide at 15 feet back from the mouth, and 
reaches a maximum height of about 15 feet. The floor 
of the cave slopes gently downward from the back wall 
to about eight feet from the mouth, where it dips very 
sharply. 
No water is at present available during the dry season 
for a distance of 15 miles from the cave, but during pre- 
historic times there may have been water seepage from 
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