Formation and Maintenance of San Bernardino Kangaroo Rat Habitat, Santa Ana River Alluvial Fan, California

The San Bernardino Kangaroo Rat (SBKR) was listed as an endangered species on January 27, 1998. The listing identified SBKR habitat on the medial and distal parts of the alluvial fan of the Santa Ana River downstream of Seven Oaks Dam that was about 77 percent completed. In 1938 about 250 cms of out-of-channel discharge transported and deposited primarily sand-sized sediment in pre-existing overbank topography formed by historic floods in the 1860s. Based on field observations and scientific literature, it appears that SBKR habitat is characterized by sandy substrate (D₅₀ 0.3 – 0.8 mm) with an average depth of 220mm, less than 20 percent grass cover, and proximity to food sources and shrub cover. Based on the hydrologic record and geomorphological and sedimentologic evidence on the fan, significant SBKR habitat-forming events have occurred twice in the last 140 years, which suggests that the frequency of habitat formation is on the order of 60 to 70 years. SBKR habitat can be created in the post-dam period by structural modifications of the main channel of the Santa Ana River that will deliver flows into the medial and distal parts of the fan, provided that an adequate supply of sand-sized sediment is available.