20 VEGETATION OF A DESERT MOUNTAIN RANGE. 
reticulata, Baccharis sarothroides (batamote), Franseria ambrostotdes, 
Lycium fremontii, Verbesina encelioides, and Bebbia juncea. 
In the cafions and arroyos large enough to have a heavy flow of 
storm water but not large enough to have even pools of water which 
are constant throughout the year, there may be found several additional 
species of plants which also occur on the sandy flood-plains of the 
largest cafions. Prominent among these are Chilopsis linearis, Hymeno- 
clea monogyra, and Baccharis glutinosa, all of which are large shrubs 
or in the case of Chilopsis may attain the size of small trees. Also 
characteristic of these sands are Franseria ambrosioides, Rumex hymeno- 
sepalus, Euphorbia pediculifera, Clematis ligusticifolia, and Calyptridium 
monandrum. 
In the largest cafions of the south side of the Santa Catalinas it is 
possible to witness the occurrence of communities of mesophilous, 
palustrine, and aquatic plants which are limited in area but are made 
up of species which stand strongly in contrast with the predominant 
forms of the bajadas. The existence of streams and pools adjacent to 
rocky slopes makes it possible in several places for Callitriche and 
Isnardia to grow within 20 feet of Carnegiea and Fouquieria. 
At the mouth of Soldier Cafion the rocky slopes of the streamway 
are clothed with typical bajada plants together with a few forms which 
are particularly abundant on cliffs and in rocky situations, both in the 
larger mountains of the region and in the volcanic hills. Among the 
latter are Opuntia bigelovii, Hyptis emoryi, Lippia wrightti, Anisacan- 
thus thurbert, Encelia farinosa, Eriogonum wrightit, Chrysoma laricifolia, 
and Crossosoma bigelovii. Among the boulders bordering the stream- 
way are Janusia gracilis, Plumbago scandens, Maurandia antirrhini- 
flora, Mimitanthe pilosa, and Stemodia plumieri, as well as occasional 
individuals of several species which are common away from streams 
at elevations of 4,000 to 5,000 feet, as, for example, Dasylirion wheeler, 
Nolina microcarpa, Erythrina flabelliformis, Ingenhousia triloba, and 
Mimosa biuncifera. When the sands of the arroyo have not been 
recently scoured by floods they support scattered individuals of Ama- 
ranthus palmeri (celite), Cassia leptocarpa, Nicotiana trigonophylla, 
Bebbia juncea, Hymenoclea monogyra, Franseria xanthocarpa, Asclepias 
linifolia, Baccharis sarothroides, Mentzelia gracilenta, and Carduus sp. 
In Ventana, Bear, and Sabino Cafions it is possible at all times of 
the year to find small colonies of palustrine and aquatic plants, and 
the vicinity of such localities is the optimum habitat for Prosopis and 
Populus. An underflow passes out at the mouth of Sabino Cafion which 
is heavier and more constant than that of any other cafion in the range; 
this gives Sabino Cajion its abundant mesophilous vegetation and also 
causes the arroyo through which its flood waters reach the Rillito to 
be occupied by a much richer stand of vegetation than is to be found 
along any of the arroyos of the adjacent region. The sandy and 
