BEDROCK AND SURFICIAL GEOLOGIC MAPPING, CLEARWATER RIVER CORRIDOR PROJECT OF THE IDAHO GEOLOGICAL SURVEY'S STATEMAP PROGRAM

The Idaho Geological Survey has been a partner in the USGS STATEMAP program since its inception in 1993. The funded projects vary in scale, scope, and geologic province, but the following themes underpin the Survey's geologic mapping program: (1) advancement of geologic understanding, (2) cutting-edge digital cartography and databases, (3) new mapping of 1:24,000-scale bedrock and surficial geologic maps, and (4) new mapping of 1:100,000-scale geologic maps to meet the long-term goal of coverage of the entire state.

New mapping of bedrock and surficial units at 1:24,000-scale along the Clearwater River corridor has been in progress for several years. Mapping is nearly complete for 18 quadrangles and part of 2 others from the Idaho-Washington border upstream to Kooskia. Bedrock mapping has refined the basement rock-basalt contact, extended or refined some of the individual basalt units, and provided more detail of the structure and petrology of intrusive and metamorphic rocks. Surficial mapping provides considerably more detailed information about the unconsolidated deposits than previous regional maps of the area. The Kamiah quadrangle is presented as an example. The Kamiah area has been geomorphically dynamic from the Miocene to the present. Large complexes of landslides indicate accumulation of sediments during times of drainage disruption of Miocene Columbia River basalt emplacement. In the Pleistocene, Missoula Floods flowed up the Clearwater valley to Kamiah, where sand deposits probably represent a delta that formed as the Clearwater River and Lawyer Creek flowed into the slackwater.

The maps give descriptions of geologic units and provide the general public, contractors, engineers, hydrologists, and governmental agencies with geologic information relevant to geologic hazards, construction needs, highway planning, land use planning, groundwater potential, and water well siting. The surficial geologic maps are available as digital web maps and are being prepared for publication, and the bedrock geologic maps are being prepared for publication as both printed paper and digital maps. Mapping of the corridor will be completed in 2004.