The recent discovery of major oil resources on Alaska's North Slope has rekindled interest in the petroleum possibilities of the Yukon-Koyukuk province, a vast tract of Cretaceous rocks stretching along the west coast of Alaska from the Brooks Range to the Yukon delta. Attention was first focused on this region in the early 1950's, after oil and gas were discovered in the Cretaceous of the North Slope by the U.S. Navy. The presence of similar Cretaceous strata in the Yukon-Koyukuk province and the possibility that some of the broad alluviated lowlands within the province might be underlain by Tertiary basins were pointed out by Gryc and others (1951) and Payne (1955). Between 1954 and 1961 large parts of the province were reconnoitered by oil company surface parties and a small amount of geophysical work was carried out in the Nulato-Kateel and Bethel areas. The explorational activity culminated in 1960-61 with the drilling of two deep tests, a 12,000-foot hole near Nulato on the Yukon River and a 15,000-foot hole at Napatuk Creek in the Yukon-Kuskokwim Coastal Lowland. Apparently neither test revealed oil shows or favorable reservoir rocks, as exploration and leasing activity in the province declined sharply thereafter.
Since 1954 the U.S. Geological Survey has maintained a modest but continuing program of reconnaissance geologic mapping of the province and its borderlands. Nearly all parts of this vast area have been visited either by helicopter or river boat. Although information in many places is still sketchy, the broad outlines of the surface geology are now known. Subsurface data, however, are almost totally lacking.
The mapping indicates that the petroleum possibilities over most of the province are limited because of complex structure and scarcity of promising reservoir rocks. Two areas where further exploration seems warranted are the Yukon-Kuskokwim Coastal Lowland and the western part of the Kobuk-Selawik Lowland.
