Located 2.5 miles south of Loomis, the Sinlahekin unit�s 14,314 acres include 480 acres leased from Washington Department of Natural Resources (DNR), 2,834 acres owned by the U.S. Bureau of Land Management (BLM), and 11,000 acres owned by WDFW. The Sinlahekin lies primarily within the Sinlahekin Valley, a north�south-running, deep, glaciated valley with sheer rock sidewalls rising from the valley floor, which ranges from about one-half to one mile wide. The property is within both the Sinlahekin Creek and the Coulee Creek watersheds. Sinlahekin Creek is the major flowing water body, while Coulee Creek goes underground most of the year. There are five impoundments and several natural ponds. Dominant habitat types are shrub steppe (bluebunch wheatgrass, big sage, bitterbrush, serviceberry), wetland (hawthorn, water birch, mountain alder, grass/sedges), and dry forest (Ponderosa pine, Douglas fir).
WDFW farms about 145 acres for wildlife forage under two sharecrop agreements, and four grazing permits are used to manipulate vegetation.
The Sinlahekin has more than 510 vascular plant species (including nine rare ones), over 215 species of birds, 60 species of mammals, about 20 species of reptiles and amphibians, over 25 species of fish, and over 90 species of butterflies. Mule deer, bighorn sheep, moose, black bear, cougar, waterfowl, wild turkey, forest grouse and rainbow trout contribute to the popularity of hunting and fishing here.