Puget Sound, WA to northern Baja California, Mexico [1, 2, 3].
Within the MSPA, found in MUs 3, 4, 5, 6, 8, 9, 10, and 11 . Important Conservation Areas of medium and high priority for turtles include Jamul Creek, middle Sweetwater River, Pine Creek-Hauser Canyon, San Diego River, Santa Ysabel Creek, Upper San Dieguito River, Upper Santa Margarita River, San Luis Rey River, and Agua Hedionda Creek.
Slow moving permanent or intermittent streams, small ponds, small lakes, reservoirs, abandoned gravel pits, permanent and ephemeral shallow wetlands, stock ponds, and sewage treatment lagoons. Emergent basking sites, vegetation and suitable terrestrial shelter and nesting sites characterize optimal habitat. Adjacent upland areas provide overwintering and estivation sites [3, 5].
Two subspecies of western pond turtle are recognized, E.m. marmorata (San Fransisco and Sacramento Valley northward) and E.m. pallida (south of San Fransisco). Four distinct mitochondrial clades have been identified: (1) Northern (2) San Joaquin Valley (3) Santa Barbara (4) Southern [6,7]. Additionally, recent genetic studies by USGS suggests SW pond turtles are distinct between watersheds in S. Calf .
Activity is dependent on temperature, with most activity when water temperature above 15ºC; courting and mating observed February - November [3, 9].
Females may reproduce at 4-8 years of age; most nests are within 50m of edge of water; clutch size varies from 2-13 eggs; incubation times vary from 94-122 days in wild [3, 9].
Feeds on larvae of dragonflies, mayflies, stoneflies, caddisflies, midges, beetles, plus crayfish, other aquatic invertebrates and vegetation; will scavenge on fish, frogs, and toads .
Occupies small home range in streams but larger area in uplands; females move shorter distances than males (149m vs 367m, mean values) [3, 12].
Human activities (e.g., recreation, collection, roads), water quality, drought, non-native turtles, native and non-native predatory species (e.g. bullfrogs, large-mouth bass, coyotes, raccoons, opossums, sunfish, crayfish, carp, mosquitofish) . Feral pigs may eat young turtles and their rooting can impact pond turtle habitat .
Excerpted from the Western Riverside Co. MSHCP (see  and citations within) - Destruction of suitable habitat appears to be the biggest threat to populations of the western pond turtle. Today, the only extensive populations remaining are in northern California and southern Oregon. In recent years, the southern California pond turtle population has experienced an alarming decline. Between Ventura County and the Mexican border, known localities have decreased from 87 in 1960, to 57 in 1970, and as of 1987, only 10 of 255 sites inspected were thought to support reproductively viable populations. Fifty-three of the 255 sites inspected contained pond turtles, the distribution of these sites follows: 25 in Ventura County, 10 in Los Angeles County, eight in San Diego County, four in Orange County, three in southwestern San Bernardino County, and three in western Riverside County. Conservation management of aquatic turtles should include not only protection of aquatic habitat, but also preservation and restoration of dispersal corridors and adjacent terrestrial habitat (potentially 500 m or more from the wetland boundary) for nesting, hibernation, and estivation (Holland, 1994; Burke and Gibbons, 1995). These corridors should also be protected from impacts associated with exotic plant and animal species, new road construction, cattle and off-road vehicle use. Reintroductions and the establishment of satellite populations would also contribute to the protection of the pond turtle.