September. Snow occurs in the higher elevations during 
the winter. The plateau top of the Sierra Madre Occi- 
dental is clothed with a fairly pure stand of open pine, 
which covers the ridges and descends to the bottoms of 
the upper canyons. The lower canyon slopes and basins 
have a characteristic Juniper-oak-agave association. 
109° 108° 107° 106° 
32° | |_ _3pe 
U S l A | 
on nn er -- >) EL PASO 
i] 
' 
qcondes C. JUAREZ is 
” 
aaa |: a i rr o 
\ r 
31° \ fe} 31° 
1 @{CHIHUAHUA 
x 
\z fe NUEVO CASAS GRANDES 
| Netdes 
Fe SWALLOW CAVE 
SKA e pa CAVE VALLEY) ooo coe 
u! : TAU CAVE 
Beg ay OLLA CAVE ae 
— EL CONCHO-DARK CAVE 
yi . PARTS OF THE STATES OF 
a SONORA AND CHIHUAHUA 
% | ae MEXICO ies 
Map of parts of the states of Sonora and Chihuahua, Mexico, show- 
ing the location of the five caves from which the archaeological maize 
described in this paper was collected. 
Four of the caves from which maize specimens were 
collected are located in a canyon of the Rio Piedras 
Verdes in Chihuahua, known to local inhabitants as Cave 
Valley. This is an area which presented almost ideal liv- 
ing conditions to the Indians who formerly occupied it; 
today it is settled by Mexican farmers. The interbedded 
volcanic formations that border the Piedres Verdas have 
weathered in varying amounts to produce numerous 
caves and ledges, many of which were occupied by the 
[ 1538 | 
