1917] VESTAL—FOOTHILLS VEGETATION 371 
soil vary from those of coarse granite-gravel to the variously sized 
blocks of rock talus. 
The shrubs are 2-5 ft. high, very loose in habit, with few branches and 
reduced leaf surface. The fruits are provided with long plumed awns. e 
plants are separated, being regularly spaced like the pinyons, the intervals 
likewise varying with degree of exposure. The habitat relations of Cercocarpus 
are in fact quite like those of the pinyon, and it is north of the pinyon area that 
the mountain mahogany association is best developed. The interspaces 
Fic. 6.—Open grove aspect of oak assemblage, caused by entrance of grazing 
animals, ca Park; open mixed grassland in coarse soil occupies foreground. 
between plants may be almost bare, or may be occupied by a sparse growth of 
xerophytes, most of them plains plants or representatives of the primitive 
grassland, the mat growth-form being common 
ARCTOSTAPHYLOS ASSOCIATION 
Cow Les (3, p. 367) and Gates (6, p.-306), Lake Michigan dunes; Wuit- 
FORD (26, p. 298), northern Michigan. In the Colorado foothills: RoBBins 
(16, p. 44); SCHNEIDER (21, p. 299); SHANTZ (22, p. 186). 
The Arctostaphylos-Juniperus association of the northeastern 
coniferous forest region is very well known to students of vegetation. 
Practically the same community is represented in the Rocky Moun- 
tains, associated there as elsewhere with coniferous vegetation. 
The same plant species and the same creeping habit are seen. The 
