Vol.11 HiiJl. — Botanical Survey of San Jacinto Mountain. 39 



The influence of these desert winds is similar to that of slope 

 exposure and, coming as they do from the east and northeast, 

 they carry the life zones up on those sides of the peaks and 

 ridges where we should naturally expect to find them dipping. 

 That warm winds may be more potent than slope exposure in 

 their effect upon vegetation is shown by the fact that on the 

 south and west slopes of the main mountain the lower limits of 

 the Yellow Pine belt follows rather closely the 5000-foot contour 

 line and dips considerably lower than that along the streams, 

 while on the east side, just below Tahciuitz and Round Valleys, 

 it is carried u]) to al)0ut 6000 feet, and in some places even 

 higher. In Tahquitz Valley the termination of the coniferous 

 forest is exceedingly abrupt. We pass down the valley in the 

 shade of Incense Cedars and Yellow Pines until an altitude of 

 6000 feet is reached, when the vegetation suddenly changes to 

 that of the Upper Sonoran Zone, the most conspicuous perennials 

 being Aclenostonia fascicnlatum, A. sparsifoUum , Diplacns longi- 

 florus, Eriodictyon tomentosum and Nolina Parryi. The abrupt- 

 ness of this change is due in part to the topography, the slope 

 taking a sudden dip at this place. 



A complicated case showing the effect of slope exposure, 

 desert winds and protecting ridges, is the following. On the 

 northwest side of San Jacinto Mountain is a basin known as 

 Hurley Flat (alt. 3500 ft.) surrounded on the north and east 

 by low spurs, on the southeast by considerably higher ridges, and 

 on the south and southwest by a continuation of Fullers Ridge, 

 which maybe designated as Schains Ridge (alt. 5200 ft.). On 

 the eastern wall of this basin (the west side of the low spur) the 

 pine belt extends dow^n nearly to the bottom. Along the south 

 wall it creeps gradually up as we proceed westward, until on the 

 southwest side of the basin (the northeast slope of Schains 

 Ridge) t^ere are no pines whatever. Passing over the summit 

 of this ridge we find a narrow belt of conifers fringing its south- 

 west side. 



In searching for the cause of this peculiar distribution we 

 notice the following. The eastern side of the basin is protected 

 from desert winds by the low spur and is therefore able to 

 support a scant coniferous growth; the winds glide over this 



