It was formerly found in Canada (in British Columbia), but in May 2002, the Canadian Species at Risk Act listed the Pacific pond turtle as being extirpated.

Adult western pond turtles are sexually dimorphic, with males having a light or pale yellow throat.

The western pond turtle originally ranged from northern Baja California, Mexico, north to the southern regions of British Columbia, Canada.

The western pond turtle is now rare in the Willamette Valley north of Eugene, Oregon, but abundance increases south of that city where temperatures are higher.

A. marmorata can be encouraged to use artificial basking substrate, or rafts, which allows for easy detection of the species in complex habitats.

Overwintering sites can sometimes be 500 meters from a main body of water [6] The western pond turtle is omnivorous and most of its animal diet includes insects, crayfish, and other aquatic invertebrates.

Raccoons, otters, ospreys, and coyotes are the biggest natural threats to this turtle, its eggs, and hatchlings.

After the goldrush in California a large "fishery" emerged processing turtles from the San Francisco Bay Estuary into canned soup for markets East.

With the removal of ponds, modification of sandy banks needed for egg laying, draining of wetlands, this species is now vulnerable.

The female usually leaves the water in the evening and may wander far before selecting a nest site, often in an open area of sand or hardpan that is facing southwards.

Females spend considerable time covering up the nest with soil and adjacent low vegetation, making it difficult for a person to find unless it has been disturbed by a predator.

The vast majority of western pond turtle hatchlings overwinter in the nest, and this phenomenon seems prevalent in most parts of the range, especially northern areas.