1917] VESTAL—FOOTHILLS VEGETATION 369 
valleys than in the foothills proper; they range into finer soils than 
do the pines. In the foothills as well as at the mountain-front the 
oaks may share mixed rocky slopes with local representations of 
Cercocarpus, pinyon, rock pine, or grassland associations, or may 
alternate with them. The extent to which they replace the rock 
pine on south-facing foothill slopes is appreciable even north of 
Perry Park, and is increasingly considerable southward. There 
is no apparent reason why they would not grow north of their 
—Alternation of mixed pms and oak forest, west of Castle Rock, 
July rox “tall herbs conspicuous at bor 
present limits in the mountain-front; some of them extend north 
on the west side of the range-crest even into Wyoming (fig. 5). 
e taxonomic condition of these oaks is one of confusion. RYDBERG’s 
Flora of Colorado (19) lists 11 species, all occurring at or near the eastern 
mountain-front. Quercus Fendleri appears to be distinct, much more xero- 
phytic, more southerly in distribution. The intergradations with most of the 
others are such that specific determinations are very difficult. CLEMENTS 
mentions Quercus Gunnisonii as the chief species of the Manitou vicinity. 
Certain Colorado botanists now speak of the doubtful oaks collectively, for the 
present, simply as Quercus spp. The writer has thus far not been able to 
distinguish different habitat groups within these Quercus spp. (cf. SHANTZ, 22, 
P. 179). 
