Ground-water resources of Baker Valley, Baker County, Oregon

Abstract

The Baker Valley is the southern part of a small oval-shaped inter-montane structural basin located near tie southeastern edge of the Blue Mountains of northeastern Oregon. The Powder River enters and leaves the valley through narrow rock gorges. The alluviated basin floor at an altitude of about 3,400 feet is bounded by high, Alpine-type mountains on the west and by lover hilly ridges on the north, east, and south. Creeks descend across alluvial fans from the higher western margin of the valley to the Powder River on the valley floor. The valley floor and the contiguous alluvial slopes are formed of unconsolidated deposits of Quaternary age having a thickness of more than 700 feet in the central part of the valley. The surrounding higher lands are formed of consolidated rocks composed of volcanic flows, tuffs, and partly consolidated deposits of Tertiary age, and sedimentary, igneous, and metamorphic roots of late Paleozoic age. The unconsolidated materials underlying the alluvial slopes are mostly fanglomerates - composed of partly consolidated angular rock fragments imbedded in assorted finer materials - and fine-grained sedimentary deposits having much inter-bedded gravel and sand along the valley floor. The unconsolidated deposits contain a body of ground water, the upper surface of which is called the water table. The water table slopes down gradient approximately parallel to tile land surface. Variations in the general inclination of that water table indicate that drainage on different segments of the alluvial slope is influent and effluent to the ground water body. Yields from wells in the fanglomerate along the rest side of the valley are not large, but large yields are obtained from wells on the valley floor just north of Baker. Properly constructed test wells have not been drilled over much of the northern part of the valley floor. The Tertiary rocks of both volcanic and sedimentary origin along the margin of the valley east of Baker contain some ground water under sufficient pressure to cause wells to flow at the surface, but generally those strata are not highly productive. Some water occurring along fault lines in these rocks has all abnormally high temperature. The growing season in this area is short and the use of shallow water for irrigation may aid materially in securing the maximum returns of which the valley is capable.