Ground-water resources of the Rogue River Basin, Oregon

Abstract

The Rogue River basin, as area of about 5,060 square miles, comprises much of the southwestern corner of the State of Oregon. It is mountainous and its arable lands are largely confined to the valley floors along the middle reaches of the Rogue River and its main tributaries, the Applegate and Illinois Rivers and Bear Creek. In these valleys, level farming lands and an equable climate afford hospitable localities to a moderate population. Although mainly an agricultural economy, lumbering, mining, and tourist trade are also economic mainstays of the inhabitants. The average annual precipitation on the valley floor is about 21 inches, but it is progressively greater with higher altitudes and reaches 87 inches in the Coast Range to the west and 60 inches in the Cascade Range to the east. The frost-free season averages 176 days in the valleys with frosts seldom occurring later than May or earlier than October. The principal farm crop of the basin is soft fruit, mainly fancy pears. Beef and dairy herds are important in the Applegate and Illinois River valleys. The rocks which underlie the basin range from Paleozoic to Recent in age. The best water-yielding rocks are the alluvial deposits of Pleistocene and Recent age and the weathered parts of several granitic masses. Of 1,035 wells visited, only 52 were drilled exclusively for irrigation. Due to the inadequate yield, a number of these wells were not in use at the time of the field investigation. The quality of the shallow ground waters is generally good, but the deeper ground waters in many places are too saline for common use. The boron and fluorine content of the ground water from some of the deep wells in the Umpqua and Chico formations is sufficient to render it unsuitable for some uses. Properly constructed and developed wells in the Agate Desert gravels and in the older alluvium of the Illinois River valley will yield small and moderate supplies of ground water for irrigation. The younger alluvium in places will yield moderate amounts of water to large open wells, locally called "sumps." The weathered part of the granite rock underlying the Grants Pass and Tolo localities yields water sufficiently for small and moderate irrigation and industrial supplies. The other rock formation of the basin commonly yield water sufficiently only for domestic supplies. In many places these rocks are so lacking in permeability that many drilled wells have failed to obtain even adequate yields for household supply.