584 Part IV. Chapter 3. 
alpinum, C. arvense, Saxifraga debilis, S. caespitosa, S. flagellaris, S. nivalis, Silene acaulis, 
Cystopteris fragilis, Oxyria digyna, Festuca brevifolia (= F. brachyphylla), Sagina Linnaei (=. 
saginoides), Stellaria umbellata (Alsine baicalensis), Thlaspi alpestre, Trisetum subspicatum and 
Sibbaldia procumbens. 
D. Mohave District. 
This phytogeographic district comprises the Mohave Desert and adjacent 
territory including Death Valley and Ralston Desert. 
The Mohave Desert lies on the north side of the San Bernardino Range 
and its continuing spur on the Chuckawalla Mountains which ranges separate 
it from the Colorado Desert on the south. It is limited in an eastern direction 
by the Colorado River and in a northeastern direction by the Kawich and 
Desert Mountain ranges. Its whole surface is cut up by short isolated ranges 
and “lone mountains” which are surrounded by sloping mesas, or enclose 
basins whose lowest portions are occupied by dry lakes. Some of these are 
level expanses of hard plastic clay, smooth and bare as a table-surface and 
bordered by a narrow strip of nitrophilous vegetation. Receiving the scanty 
rain water that runs down from the bare hill about them, they at times may 
be transformed into tenacious mud, or covered at times with a few inches of 
water‘). Or the surface layers of these desert basins may consist of what pro- 
spectors call *self-rising soil”, a loose alkaline powder slightly crusted over, Of 
a snowy incrustation of soda salts. — The flora of the Mohave District 
shows a marked influence of the vegetation of the Nevada, or Great Basin 
District, and for this reason it has been placed in the classification as a part 
of the Great Basin phytogeographic region, distinct from that of the flora of 
the Sonoran deserts to the south. The difference in the character of the two 
floras is only in part due to climatic causes, but it is largely influenced by the 
topography of the country. In the case of the Mohave Desert, the migration 
current from eastern Utah and Nevada would meet with no considerable ob- 
stacle until it reached the San Bernardino Range and its continuation. The 
distinctness of the two desert floras is further emphasized by a consideration 
of the zonal distribution of their respective floras. 
The Larrea belt is presented in both the Mohave and Colorado Desserts. 
But, however, useful this shrub (Zarrea mexicana = Covillea tridentata) may 
be as the biologie index of larger divisions, it is of less importance in the 
study of smaller areas. Above the Larrea belt of the two deserts occUf 
in the Mohave Desert a belt of Yucca drevifolia (3000—4000 feet = 9157 
ı220 m). In its normal limits Juniperus californica is mingled with the yuccy 
but does not accompany it far above them. The piion belt is above the 2 
yucca belt and is characterized by the presence of Pinus monophylla between ° 
4000 and 6000 feet (1200—1830 m). In the upper end of Antelope Valley, E 
according to PARISH, the orographic confusion there has given rise to a phyto 
ı) PARISH, S. B.: A sketch of the Flora of southern California, Botanical Gazette XXXVI: 206. 4 
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