Geology and Geomorphology
The majority of the Crooked River basin lies within the Western Glaciated Plains Natural Division with a small area near the mouth in the Big Rivers Upper Missouri Natural Division (Figure Ge01)(Thom and Wilson 1980). The entire basin is in the Dissected Till Plains and is near the southern edge of the area covered by glaciers (Detroy and Skelton 1983). The basin topography consists of rolling to hilly glacial plains with narrow ridges and steep side slopes. The Missouri River flood plain near the mouth of the Crooked River is extremely flat and poorly drained.
Geology and Soils
The basin is underlain by Pennsylvanian-aged formations consisting primarily of sandstone, shale, limestone and thin seams of coal (Figure Ge02)(Detroy and Skelton 1983). The bedrock slopes from the southwest to the northeast underneath the basin. Large areas of Bethany limestone are found in the western part of the basin (Preston 1986). The lower Crooked River basin is underlain by the Lexington coal field (MDNR 1986a).
Most basin soils are formed from glacial till (a mixture of clay, rock, gravel and sand), alluvium (water deposited soil) and a windblown silt called loess. The soils have their origin in the four periods of continental glaciation with deposits from the final glacial advance (Kansan) overlying earlier deposits. After glaciation a thick layer of loess was deposited over the basin creating a relatively level drift plain (USDA-SCS 1982). Weathering over several thousand years has produced dissected glacial till plains overlain by loessial soils. Loess deposits decrease in thickness from southwest to northeast across the basin. (Preston 1986). Loess deposits range from 32 feet deep near the Missouri River to about eight feet deep near the headwaters (MDNR 1995). Loessial soils cover broad, gently sloping ridges of silty loam and are suitable for farming. Glacial soil occurs on steeper, eroding slopes and it is a less productive brown loam or gritty silt loam. Glacial deposits overlie limestones and shales and are generally less than 100 feet thick (MDNR 1995). Valleys are covered with alluvial silt and clay loams, and are the most productive soils in the basin. Areas where surface soil has been eroded and subsoil has been exposed are less productive (USDA-SCS 1982).
The Crooked River is a sixth order river with a basin area of 335 square miles (214,790 acres; USDA-SCS 1982). The Crooked River basin is bordered by the Fishing River basin to the west, the Wakenda River basin and Moss Creek to the east (all minor Missouri River tributaries) and the Grand River basin to the north. The basin has a maximum width of about 20 miles. The flood plain width varies from 500 feet in the upper reaches to about one mile in lower sections of the basin (NRCS field exam report). The Crooked River mainstem is about 70 miles in length and runs from northwest to southeast.
Channel gradients for most of the Crooked River watershed were reported to range from 5 to 50 feet per mile in 1976. The gradients found in the Missouri River bottom area were about 1/2 foot per mile (NRCS field exam report). Based on current topographical maps, average gradients in the Crooked River basin range from 5 to 138 feet per mile. Stream gradient information for fourth order and larger streams in the Crooked River basin can be found in Figure Ge03.