The area now occupied by Fort Boise Wildlife Management Area is interesting geologically and historically. The WMA is situated at the confluence of the Snake and Boise rivers and is just downstream from the mouth of the Owyhee River.
Prior to dam construction, the combined rivers in-flood had a great effect on the landscape. The soils on the WMA are patchy and variable, changing from gravel to sand to silt, all within less than 100 meters; this is typical of alluvial soils formed by the deposition and erosion of rivers. Many soils on the WMA are poorly drained and alkaline with sodic crusts. The plants on the surface reflect the soil profile below. Greasewood and saltgrass predominate in high pH zones, while willow, non-native hardwood trees, and black cottonwood are found in the extensive gravelly riparian areas formed by the Boise River, which delineates 2.35 miles of the southern WMA boundary. Big sagebrush (Artemisia tridentata) is found in the limited, more arable upland soils, and small acreage row crops were grown in the mid-20th century. Due to the variable soils, most of what is now Fort Boise WMA was used as irrigated pasture or seen as ‘waste ground’ after European settlement.
As rivers do not down cut into gravels significantly, they typically spread out to form many braided channels and islands, and this is the case where the Boise River meets the Snake River. The many wide, gravel-bottomed channels below the Boise River mouth form a natural ford. Native Americans greatly valued the gravely shallows for the abundant spawning salmon and the ford was a main Snake River crossing on the Oregon Trial. The vicinity of the three rivers was pivotal in the early fur trade and hosted some of the oldest European settlements in the west. A Hudson Bay Company fur post, “Fort Boise”, was located somewhere near the mouth of the Boise River, from the 1830s to the mid-1850s. With the demise of the fur trade, the Fort remained to sell provisions to hundreds of travelers on the Oregon Trail.
The Fort Boise WMA was established in 1959 when Idaho Power Company deeded 330-acre Gold Island in the Snake River to Idaho Fish and Game as partial habitat loss mitigation for the Hell’s Canyon dams. Starting in 1960, a series of mainland purchases by the department added small to medium sized parcels to Fort Boise WMA. The last of these purchases, the 95-acre Mann purchase, occurred in 1991 and brought the total Fort Boise WMA acres to 1,548.
Roswell Marsh Wildlife Habitat Area began in 1986 with a 150-acre Idaho Fish and Game and Ducks Unlimited acquisition. The department purchased the remainder of the property, the 35- acre Barnard segment (along with shares of Riverside Ditch irrigation water) and the 475-acre Hurtt parcel in 1988. Development of the 185-acre wetlands complex was completed in 1991 when three miles of diking and water structures were installed. In 2003, the Riverside Irrigation District ruled that water from the Riverside ditch, the Roswell Marsh WHA wetland water source, could only be used for ‘agriculture’ and that ‘wildlife’ use, the highest water use under Idaho law, was prohibited. After several years without water, the area was flooded again in 2009 when a permit for a large underground well was secured and water was pumped into the wetland.