The Yulupa Creek watershed comprises an area of approximately five square miles, and is considered a viable steelhead, Oncorhynchus mykiss, spawning habitat; stream surveys conducted from 1966 to 1986 indicated significant, but declining populations of anadromous fish.

[5] Land use in this watershed consists of Annadel State Park usage and very low density rural single family residential development, much of which is upmarket housing stock.

In addition to known spawning area for O. mykiss, Yulupa Creek has been designated as a high quality riparian zone and an identified habitat of freshwater shrimp.

[7] An unusual characteristic of these forests is the high content of undisturbed prehistoric bunch grass understory, testifying to the absence of historic grazing or other agriculture.

In the oak woodlands, the dominant understory plants are native bunch grass, toyon, blackberry, western poison-oak and in drier patches coyote brush.

One of the major soil associations within the upper elevation riparian zone is Goulding cobbly clay loam, which contains roughly 25 percent cobblestones, as well as some basaltic exposures, betraying the volcanic past of the Sonoma Mountains formation.

Much of the soil type in the Yulupa Creek riparian zone consists of Laniger loam, with rhyolite outcrops, another relic of the igneous history.