Named for Imuruk Lake. Type locality designated in canyon of Kugruk River, 3 mi below Imuruk Lake, Bendeleben C-2 quad, Seward Peninsula, west-central AK. Imuruk Lake occupies vaguely defined graben whose bounding faults displace lavas of Imuruk volcanics. Unit consists of group of basaltic lava flows and associated agglomerate cones, brecciated by frost action and mantled by silt 3 to 20 ft thick. Thickness varies widely; individual flows are as much as 150 ft thick. Overlies deeply weathered lava flows of Kugruk volcanics (new); underlies Gosling volcanics (new) which overlies silt mantle of Imuruk. Lava flow of Gosling volcanics has invaded canyon excavated into and below Imuruk volcanics. Age is probably early(?) Pleistocene and middle Pleistocene based on probable relationship to glacial intervals.

Source: GNU records (USGS DDS-6; Menlo GNULEX).

Distinction between Kugruk and Imuruk Volcanics is invalid; a single volcanic sequence is represented. Name Imuruk Volcanics is retained for sequence and name Kugruk Volcanics is abandoned. K-Ar age on basalt collected at Lava Camp Mine is 5.7 +/-0.2 Ma; this flow is Pliocene age. Age of Imuruk Volcanics is therefore late Tertiary to middle Pleistocene.

Source: GNU records (USGS DDS-6; Menlo GNULEX).