In the vicinity of Big Pines, on the interior slope, these gophers preferred broken forest where snow brush or other brush occurred; their workings, however, were also found beneath groves of conifers and black oaks. The abundance of earth cores resting on the duff indicated that this species is active in the snow in winter. _Specimens examined._--Total, 5, distributed as follows: Los Angeles County: 2 mi. E Valyermo, 4600 ft., 2; 3 mi. W Big Pines, 6000 ft., 1; 1 mi. S and 2 mi. E Big Pines, 8000 ft., 2. =Thomomys bottae mohavensis= Grinnell Valley Pocket Gopher One specimen of this subspecies was taken on December 31, 1951, in the Joshua tree belt, eight miles east of Llano, 3700 feet elevation. Family HETEROMYIDAE =Perognathus fallax fallax= Merriam San Diego Pocket Mouse This pocket mouse is restricted to the coastal sage scrub association, and was recorded from Cajon Wash west to Live Oak Canyon. The mouse does not inhabit even the lower edge of the chaparral belt, but in the coastal sage flats is usually the most abundant rodent. In disturbed parts of the coastal sage belt _fallax_ is less common, and was never trapped in channels of rocky washes. Trap lines in the eroded adobe banks of the foothills, where white sage and coastal sagebrush are the dominant plants, took mostly these pocket mice. Although the soil of such slopes is compact and seemingly is unsuitable for burrowing by heteromyids, _fallax_ is the most common rodent. Because few burrows of pocket mice were noted there, it is possible that the many old unused burrows of _Spermophilus_ and _Dipodomys_ which honeycomb certain parts of adobe banks are used also by _fallax_; some of these burrows shelter _Peromyscus eremicus_ and _Peromyscus californicus_. These mice are inactive above ground in cold weather. In the sage belt near Thompson Canyon, where this subspecies had been found to be the most common rodent, none was trapped on the sub-freezing night of December 3, 1948, although other rodents were found in usual numbers. Individuals have been taken on nights of intermittent rain, yet none has been trapped on freezing nights. This species is characteristically heavily infested by a large species of mite. Usually these mites congregate around the base of the tail. On October 11, 1949, one lactating female and two carrying embryos were taken. _Specimens examined._--Total, 11, distributed as follows: Los Angeles County: 4 mi. N and 1 mi. E Claremont, 1900 ft., 5; 3 mi. N Claremont, 1600 ft., 6 (5 PC). =Perognathus fallax pallidus= Mearns San Diego Pocket Mouse