68 BOTANICAL FEATURES OF NORTH AMERICAN DESERTS. 
The salient features of the representation are: 
1. The wide extension northward and eastward of the Gulf of Cali- 
fornia; northward up the valley of the Colorado River to and into the 
Grand Canyon and into Nevada; eastward to the upper Gila and the Salt 
River. 
2. The deeply indented and rocky coast-line of Arizona, with many 
estuaries and bold headlands. 
3. The insular condition of the region of Tucson east and west of the 
long valleys of the Santa Cruz, of the San Pedro and Sulphur Springs, 
forming a veritable archipelago in which the Santa Catalinas, the Rincons, 
the Santa Ritas, the Huachucas, and the Tucson Mountains formed promi- 
nent islands, while Tumamoc and other basaltic hills were under water. 
4. The southern coast ranges of California disappear under water, 
while the southern end of the Sierra Nevada appears as a long, narrow 
promontory disconnected at the Canada de las Uvas from the Sierra 
Madre, and at San Bernardino from the San Jacinto and Peninsula Range 
of Mountains. 
ASPECT OF THE VEGETATION ABOUT TUCSON. 
The secondary maximum of precipitation in southern Arizona occurs 
in December and January, and amounts to 2 or 3 inches during these two 
months. On the higher levels this comes in the form of snow, and gener- 
ally melts under the noonday sun and is almost entirely absorbed by the 
soil, thus yielding the greatest efficiency in promoting the growth of plants. 
At levels between 2,000 and 3,000 feet, vegetation begins to awaken in 
January and a large number of forms begin to bloom early in February, 
and mature fruit in March and April with the diminution of the rainfall. 
In all of this winter wet season, as it may be termed, the checking action 
is due to the low night temperatures, which drop to 30° and even 20° F. 
on many occasions; and a few warm days may bring a luxuriant crop of 
low herbaceous annuals almost to bloom, which may then be blighted by 
the frost in January. In the general average of such conditions it rarely 
occurs that the more precocious forms bloom before the first week in 
February (plate 53). 
WINTER PERENNIALS. 
A large number of shrubs and species with perennial root-stocks and 
bulbs push up shoots, leaves, and flowers under the stimulus of the rising 
temperature and the moisture supply, including the following: 
Brodiea capitata, with a few blue or white flowers borne on a slender 
scape with a deeply buried bulb; Anemone sphenophylla, a relative of the 
crowfoot, with long-stalked cylindrical fruits; Penstemon wright, with 
its crimson tubular flowers, a succession of which follow through March 
and April; and P. parryi, on the slopes, with a metallic luster to the flowers. 
Stalks of the last two species are a favorite food of rock-squirrels, which 
