Ana River Springs, Oregon.
According to the United Slates Geological Survey reports, the northern end of the valley of Summer lake, in southern Oregon, contains a group of three or four large springs which unite to form Ana river, the principal feeder of the lake front the south. These springs occur in a semi-arid region, where their volume-—about 100,000 gal. a minute—and their constant flow through wet and dry seasons make them objects of unusual interest, and their source has always been a puzzle to local investigators. Summer lake valley is a depression bordered on the west and north by conspicuous cliffs of basalt and on the east by lower rims, of the same material. One large stream, Chewaucan river, rising in the wooded mountains west of the basin, discharges into it through a conspicuous canon; but the flow of this stream is less than that of the great springs at the head of the valley, and a large part of it escapes over the surface southward through Chewaucan marsh into the alkaline lake Abert, which occupies a depression somewhat lower than that partially filled by Summer lake. The surface drainage into the basin from the high, rocky, arid plateaus to the east is small. The temperatures of the Ana river waters—20° or more above the mean annual temperature of the region—indicate that the springs rise from depths 1,000 ft. or more below the surface; and, as the alluvium that forms the valley floor is probably a mere veneer, whose thickness is much less than this, it is probable that the waters rise from the underlying rocks along one or more of the lines of easy passage afforded by the faults or fracture planes that limit the valley. But, even if the springs yield rock-waters rising from depths, the source of these waters still remains unknown. The geologists of the United States Geological Survey who have been studying the region rejected at once the idea that the areas east and south of the springs could furnish the water—partly, because of the aridity of these areas, and. partly, because their investigations had revealed structural conditions that would tend to prevent the circulation of the water westward to the point at which it issues. North and west of the springs, however, is a mountainous region, not well known geologically, but including an area that is well timbered and has relatively high rainfall. In this region rise Sprague and Williamson rivers, both streams of considerable volume. It is probable that the surface of this mountain region presents areas of porous rock capable of absorbing the rainfall that falls upon it. and these areas are regarded as the most probable source of the waters that issue in such great volume at the springs.