3D MAPPING OF THE COLUMBIA RIVER BASALT GROUP (CRBG) AND THE STRUCTURAL GEOLOGY OF THE EASTERN YAKIMA FOLD BELT (YFB) AND THE WESTERN PALOUSE SLOPE: NEW STRUCTURAL FEATURES REVEALED AND EXPANDING THE EASTERN LIMIT OF THE YFB

A series of structure-contour and isopach maps for the various members of the Saddle Mountains and Wanapum Basalts of the CRBG, intercalated Ellensburg sedimentary interbeds, and suprabasalt sediment units were developed for the Columbia Basin Groundwater Management Area as part of their hydrogeologic studies for a three county area (~ 18,800 km2 area) in south-central Washington. Data used to generate these maps came from existing surface geologic mapping, 280 deep stratigraphic control wells, and the stratigraphic interpretation of nearly 3,000 water well logs. Significant results from this mapping with regards to the structural geology of this area include the discovery of: (1) the eastern extensions of the Saddle Mountains and Frenchman Hills anticlinal ridges (YFB) by 16 km and 32 km, respectively; (2) two previously unknown, broad, low amplitude, east-west-trending anticlinal folds (YFB) buried beneath the Quincy Basin suprabasalt sediment fill; (3) two previously unknown en echelon, northwest-trending, doubly plunging anticlinal folds that appear to be part of the northwest-trending Rattlesnake-Wallula alignment (the “RAW”) in the Pasco Basin; (4) a large, broad, northwest-trending anticlinal fold (south of Sentinel Gap) that may represent either the southeastern extension of the Hansen Creek structure or the southern extension of the Sentinel Gap fault; (5) a previously unrecognized major erosional unconformity between the Miocene Wanapum Basalt (30 to >50 m removed by erosion) and the Mio-Pliocene sediments of the Ringold Formation along at least a 57 km portion the eastern margin of the Columbia Basin.