1917] VESTAL—FOOTHILLS VEGETATION 365 
best developed on south-facing slopes, commonly at the bottoms of open 
canyons, beside graded roadways. Species of Gilia , Physaria, Phacelia, 
Berberis, Gaillardia, and Pachylophus are chatactetiatic Gravel slides have 
been studied by CLEMENTS, and by SCHNEWDER (21) 
The primitive grassland is closely related to certain associations 
of the Plains region, notably the mat association (9, D: 396; 34, Pp: 
393), and the Gutierrezia-Artemisia association (24, p. 398), and to 
the other primitive assemblages leading to short-grass. ‘It is more 
generally distributed, as would be expected, at lower elevations 
1G. 3.—Granite-gravel floor, with much bare surface, some primitive grassland, 
and mats * A rctosta A ylos; in background rocky summit or knob, with scattered pines; 
Flagstaff Mounta: 
and more southerly parts of the mountain region, and in the more 
exposed habitats. It probably occupies a larger proportion of the 
total area in the lower parts of the Front Range than any of the 
other associations in their unmixed condition. 
ROCK PINE ASSOCIATION 
CLEeMENTs (1); RAMALEY (10, 12, 14); Ropsrns and Dopps (18), distribu- 
tion of conifers on the mesas near Boulder; SHAntz (22, p. 184); WATSON 
(25, p. 207); Youne (28, p. 337)- 
Pinus scopulorum, variously called the rock, western yellow, 
or bull pine, is the important tree in the foothills. Its plasticity 
