OcT., 1899 } UPPER SONORAN ZONE. 53 
to fix with certainty the normal zone altitudes. Hence those here given 
must be regarded as approximate only. The average width of the belt 
of overlapping of adjoining zones appears to be about 800 feet; so that 
the normal vertical distribution of the distinctive species of each zone 
overreaches in both directions the altitudes given by about 400 feet. 
The zone positions accorded the various species are based on per- 
sonal field experience, and in the great majority of cases are believed to 
be correct; in a few instances, however, the evidence is inconclusive— 
hence the zone lists must be regarded as provisional and subject to 
correction. Species recently exterminated or driven away, as the moun- 
tain sheep, elk, and grizzly bear, are included in the tables. 
UPPER SONORAN ZONE. 
The Upper Sonoran element in the region about Shasta is dilute and 
is limited to Shasta Valley at the north base of the mountain, which it 
reaches by way of the Klamath country on the north and northeast. 
It has no connection whatever with the Upper Sonoran of the Sacra- 
mento Valley on the south, which ends near the point where Pitt River 
joins the Sacramento, about 50 miles below Shasta. 
Shasta Valley is an arid plain about 25 miles in length by 10 or 12 in 
breadth, studded with small volcanic buttes and lava flows. It varies 
in altitude from a little less than 4,000 to about 2,700 feet, and is lowest 
at the north, where the Shasta River, by which it is traversed, flows 
into the Klamath River. Shasta River is in places bordered by decid- 
uous trees, mainly Populus trichocarpa, Betula occidentalis, and Alnus 
rhombifolia. The valley is sparsely covered with rabbit brush of sev- 
eral species, mainly Chrysothumnus occidentalis and C. riscidiflorus, and 
in some places, chiefly on the east and south, by the true sagebrush 
(Artemisia tridentata). The southeastern part contains an open forest 
of junipers (Juniperus occidentalis), which meets the pine forest of the 
basal slopes of the mountain. The western part is an open plain very 
scantily dotted with rabbit brush and a few small and mainly incon- 
spicuous plants, among which were observed: Mentzelia levicaulis, 
Xanthium strumarium, Heliotropium curassavicum, Verbena bracteosa, 
Datura meteloides, Sarcobatus vermiculatus and Nicotiana sp.? Along 
the western border of the valley, near the Scott Mountains, several 
characteristic shrubs occur, among which are Ceanothus cuneatus, Arcto- 
staphylos (viscida?), Cercocarpus parvifolius, Eriodictyon glutinosum, and 
Garrya fremonti.! 
The zone position of this region is further indicated by the presence 
of such birds as the chat (Icteria virens longicauda), bush-tit (Psaltri- 
parus minimus californicus), California towhee (Pipilo fuscus crissalis), 
California jay (Aphelocoma californica), and California valley quail 
(Lophortyx californicus vallicola). Formerly antelope were common 
here, but now they are rarely seen. The most abundant mammals are 
jack rabbits (Lepus californicus), sagebrush cottontails (Lepus nut 
' Garrya fremonti is both Upper Sonoran and Transition. 
