Drawing by Robert Savannah, USFWS
The Pacific pond turtle (Clemmys marmorata) is the only native freshwater turtle in northern Baja California, California, southern Oregon and Nevada (isolated patches near Reno). This species also occurs in western Oregon and Washington and southern British Columbia,* where its range overlaps that of the painted turtle (Chrysemys picta).
Actually, Pacific pond turtles are only rarely pond dwellers. In the western United States there were relatively few ponds or lakes prior to the construction of reservoirs and farm ponds. Clemmys marmorata occurs in a variety of habitats, but my experience has shown that this turtle is most at home in streams, large rivers, slow-moving sloughs, and quiet waters. Many of its habitats are rocky, or strewn with gravel and boulders. Clemmys marmorata is remarkably well adapted to survive the aridity and annual drought of the Mediterranean climate typical of the region from southern Oregon to northern Baja California. In this portion of their range, C. marmorata populations reach high densities. Wily individuals survive times of low water levels by moving to remaining pools or pockets of moisture. For example, I found 12 adult turtles in one small pool (3 feet by 10 feet and one foot deep) along Nicasio Creek, Marin Co., California. These turtles are capable of moving long distances (at least one mile overland) and of locating remaining water sources when streams and rivers dry up in late summer. They apparently can survive droughts by digging into the mud on the bottom of water courses.
As part of my graduate studies, I spent four summers studying and enjoying C. marmorata in a stream in northern California. The turtle is secretive and wary, but through intensive search and collecting (mostly by diving) I captured and marked 578 turtles in a 2.2 mile stretch of stream. I estimated the population density at 85 turtles per acre of water (215 per hectare!). I recaptured many individuals for a total catch of 1,500 turtles over the four summers. On one occasion I caught about 50 turtles in one deep pool along the stream.
Thus C. marmorata may reach high local densities in flowing waters. Other abundant populations frequent some western waters. However, due to their elusive habits they are not easy to find anywhere in the range. The largest populations are scattered from southern Oregon to central California. Elsewhere (with a few exceptions), the species appears to be scarce. They are extremely rare in the states of Washington and Nevada.