[en] This study focuses on the structure and stratigraphy of an 80-km₂ area at the southern margin of the Pasco Basin in Wallula Gap. Field stratigraphy, petrography, natural remanent magnetism, and major-element chemistry indicate that the tholeiitic basalt flows of the Wallula Gap area correlate with units of the Grande Ronde, Wanapum, and Saddle Mountains Formations of the Yakima Subgroup of the Columbia River Basalt Group. Flows of the Frenchman Springs, Umatilla, Pomona, Elephant Mountain, and Ice Harbor Mmebers are present in the area. The Frenchman Springs Member exposed in the Wallula Gap is more than 185 m thick and consists of eight to nine flows. Its thickness and possible contemporaneous structural deformation apparently prevented emplacement of both the Roza and Priest Rapids Members at this locality. Structural uplift of the Horse Heaven Hills began prior to extrusion of the Pomona flow. Both the Pomona and Elephant Mountain Members thin and pinch out over the crest of the uplift near Mound Pond. The Ice Harbor flow was apparently confined to the basin north of the Horse Heaven uplift, but an exposure at Mound Pond suggests it flowed through Wallula Gap as an intracanyon flow. The Wallula Gap fault zone trends N65₀W and can be traced for at least 11 km along the north flank of the Horse Heaven Hills uplift. Where the fault intersects the Olympic-Wallowa Lineament at Van Sycle Canyon 8 km east of Wallula Gap, it is a broad zone of normal faulting, 300 m wide, with as much as 310 m of displacement of the basalt stratigraphy. Two faults occur in the northern portion of Van Sycle Canyon and define a graben trending N45₀W. A third fault, roughly parallel to the Wallula Gap fault, transects the The Nub and offsets 14 m of Ice Harbor basalt