There are several habitats within the coastal sage scrub association. These differ from one another chiefly on the basis of soil type. The soil of the rather level sageland in most places is rocky or gravelly, or, as adjacent to washes, it is finely sandy in texture, and supports the major plants of the association. Most of the eroded adobe banks at the bases of the foothills support these same plants, with white sage being the dominant species. Locally, as in damp hollows or cleared areas, there is grassland. Jumbles of boulders, sand, gravel, and steep cutbanks, are characteristic of the channels of dry washes, these areas supporting sparse vegetation. The fauna and flora of the washes are distinct from those of surrounding sage flats. Because they are included within the geographic limits of the coastal sage belt, however, the washes are discussed along with this association.

The abruptness with which one habitat gives way to another in this association causes sharp dividing lines between the local ranges of certain mammals. For example, in trap lines transecting dry washes and level sageland two assemblages of rodents were found. That part of the line amid the boulders and cutbanks of the wash took mostly Peromyscus eremicus fraterculus and Neotoma lepida intermedia, while Perognathus fallax fallax, Dipodomys agilis agilis, and Peromyscus maniculatus gambeli were taken in the adjacent sage flats. The steep adobe slopes of the foothills, which constitute the upper part of the coastal sage scrub association, are commonly inhabited by Peromyscus californicus insignis, which rarely occurs in the level tracts of sage a few yards away. Thus, this association is not homogeneous with regard to its rodent population; many of these species have local and discontinuous distributions.

The following list gives the results of about 500 trap nights (a trap night equals one trap set out for one night) in typical coastal sage-scrub association one-half mile southwest of the mouth of San Antonio Canyon, at 1700 feet elevation.

Table 2.—Yield of 500 Trap-nights in the Coastal Sage Scrub Association.

NumberPer cent
of total
Perognathus fallax fallax3130.7
Dipodomys agilis agilis2019.8
Reithrodontomys megalotis longicaudus44.0
Peromyscus californicus insignis44.0
P. eremicus fraterculus76.9
P. maniculatus gambeli2019.8
Neotoma lepida intermedia98.8
N. fuscipes macrotis22.0
Microtus californicus sanctidiegi44.0

The list below indicates the catch in 200 trap nights in San Antonio Wash, at 1700 feet elevation and within the realm of the coastal sage; all of the traps were set in rocky and sandy main channels of the wash.

Table 3.—Yield of 200 Trap-nights in San Antonio Wash.

NumberPer cent
of total
Perognathus fallax fallax25.1
Peromyscus californicus insignis25.1
P. eremicus fraterculus2666.7
Neotoma lepida intermedia923.1

The prickly-pear cactus is of obvious importance to certain mammals of the coastal sage belt. This cactus is most common in disturbed areas such as sandy flats bordering washes, eroded adobe banks, and land once cleared by man. In these areas it is often the dominant plant with respect to area covered, usually growing in dense patches each covering approximately 150 square feet. It provides substitute nesting sites for Neotoma lepida in areas devoid of rock piles, and is probably the major factor governing the distribution of this wood rat in the sageland. Cottontails and brush rabbits use prickly-pear cactus extensively as refuge. Their forms and short burrows can be seen beneath many of the clumps of cactus.