92 THE BOTANY OF THE CUYAMACA MOUNTAINS, 
Spiræa with some other shrubs), runs along within a mile of the © 
- beach, watered and sustained by the sea-fogs. Then comes what — 
may be called the cactus zone, as six or eight species of that — 
family, with low yuccas and other plants of the group bordering — 
the desert are the most striking growth, often forming thickets by = 
themselves in sandy places, and being in the dry season almost i ) 
the only green vegetation. The laurel sumach ( Lithrea laurina ~ 7 
Nutt.) is a shrubby tree accompanying them in thickets of small — 
extent. eS | 
These characterize the mésa, scarcely ascending above it, and — 
form indeed the northern extension of the flora of the still more- : 
arid peninsula. The river-bottoms are more fertile, many grasses, 
flowering plants and small live-oaks (Quercus agrifolia Nees), syè- — : 
amores and willows, lining the edges of the water-courses, which 
are, however, usually dry during nine months of the year, for a dis- 
tance of five or six miles above their mouths. This valley vege- — 
instead of the southern (or lower) Californian flora. Some of the 
sandy portions, however, reproduce nearly the same group as the 
Colorado valley. Of course it is quite possible that isolated spec- 
imens of some trees may exist, not met with on our journey. 
As the botanists of the Mexican Boundary, and Pacific 
Surveys have explored and thoroughly analyzed the ‘flora of t 
lower zones, I will refer to their reports for further details. 
The forests of the mountains may perhaps be best illustr: 
by giving an abstract of my observations made during Our 
_ joumey across them, at the same time giving an idea of the clima 
at the end of April.* 
April 26th. Atl P. m., we left town sd rode over the ı mi 
the San Diego river, encamping a mile above the old Mission, 
-~ — date palms and olives in cultivation give quite a tropical 
ue to the already parched and barren scene. A few pools of stag 
Se water only remain in the wide sandy river-bed. I walked 
ee camp three miles over the mésa north of the valley, to where 
— Po against the granite hill through which the river has 
de ow cañon, returning for two miles ao the lower, 
= 
