24 VEGETATION OF A DESERT MOUNTAIN RANGE. 
wrightii, Dalea wislizeni, Calliandra ertophylla, Hymenopappus mexi- 
canus, Artemisia ludoviciana, Dalea albiflora, Asclepias linifola, Fran- 
seria tenuifolia, Baccharis thesioides, Ayenia microphylla, and Anisolotus 
argensis. The commonest summer ephemerals are Eriogonum abertia- 
num and Eriocarpum gracile. 
The flood-plains and the banks and beds of the arroyos in the Upper 
Desert are, in general, more like the arroyos of the desert in their 
vegetation than like those of the Encinal region. The largest tribu- 
taries of Sabino Cafion are somewhat less rich in aquatic and palustrine 
plants than the lower portion of the cafion, and merely because of 
their steeper gradient and less regular flow. The forest which occupies 
the flood-plains of Sabino Basin is chiefly made up of Quercus emoryt, 
Quercus arizonica, Platanus wrightii, and Cupressus arizonica. The 
smaller flood-plains and arroyos of the Upper Desert have few of these 
trees but occasional individuals of Populus and open thickets of Bac- 
charis emoryt and Baccharis sarothroides, together with Franseria 
ambrosioides, Ingenhousia triloba, Erythrina flabelliformis, Croton texen- 
sis, Calliandra eriophylla, Brickeilia californica, Gymnosperma corym- 
bosa, Amorpha californica, Bouvardia triphylla, and Stachys coccinea 
(see plate 10a). 
THE ENCINAL REGION. 
Some of the distinctive species of the Lower Encinalare found at 4,000 
feet and other forms, characteristic of the Upper Encinal, extend upward 
into the Forest Region as far as 8,000 to 8,600 feet. The Lower Encinal 
may be said to have its commencement, however, in the open orchard- 
like stands of Quercus oblongifolia and Quercus arizonica, which occupy 
northerly slopes at about 4,300 feet. At an approximate elevation of 
5,000 feet the open Encinal may befound on all slopes except the steepest 
southerly ones, while on steep northern slopes it already forms nearly 
closed stands. The dense stands of the Upper Encinal region begin to 
appear on southerly slopes at about 5,800 feet, and persist to the eleva- 
tion of 6,200 to 6,400 feet, where large pines begin to dominate the 
physiognomy and the true forest may be said to begin. 
The activities of growth and flowering which are so conspicuous on 
the Desert in the season of winter rains are very much reduced in the 
Lower Encinal and are practically absent in the Upper Encinal. 
Leaves are retained by the evergreen oaks and the sclerophyllous shrubs 
throughout the winter and are shed in April or May, simultaneously 
with the first growth of shoots and the renewal of foliage. Extremely 
few of the ephemerals which often carpet the Desert in January are 
to be found in the Encinal region. There is some activity on the part 
of root perennials in the Lower Encinal during the months of March 
and April, and flowers may be found on species of Spheralcea, Calo- 
chortus, Verbena, Pentstemon, Eriogonum, and Lesquerella. Such activ- 
ity is commonly stopped by the advent of the arid fore-summer, and 
