Main tributaries draining into the Cowlitz River on or near the wildlife area are the Cispus and Tilton rivers. Large-scale flooding occurs in the Randle Valley when rain on snow events couple with a high water table, which contributes greatly to the hydrology of the wetlands located on the wildlife area. The majority of the land base can be classified into one of four habitats – emergent wetland, riparian/forested wetland, coniferous forest, and mixed deciduous forest. In addition, several forage pastures are maintained.

The Cowlitz River historically supported rich runs of anadromous salmonids such as spring and fall Chinook, coho, steelhead and cutthroat trout. Most of the natural production of these fish occurred in the upper Cowlitz River watershed above Mayfield Dam. Since the majority of the Cowlitz Wildlife Area exists between the barrier dam at the Cowlitz Salmon Hatchery and the base of the Cowlitz Falls Dam, the wildlife area provides no major benefits to anadromous fish. The exception is the Kiona and Spears units near Randle which have the potential to provide access to additional spawning/rearing habitat.

A 50-300-foot buffer zone around Riffe and Mayfield Lakes, surrounded mostly by private land, makes up 30 percent of the wildlife area, although it is not considered part of any unit. The zone is managed to protect bald eagle and osprey foraging habitat and emergent wetlands, and to protect it from illegal timber cutting by private landowners who wish to improve their views of the lakes. It is accessible only by boat, except at the Kosmos unit. Some camping is possible at the east end of Riffe Lake depending on the water level. Around Mayfield Lake, the buffer is interspersed with Tacoma Power recreational land.