Page:Centennial History of Oregon 1811-1912, Volume 1.djvu/251

 will liiul it fully considered in the Chap- ter on "The Willamette Sound" in I ho Two Islands, by Prof. Condon.

On our map j'ou will find his Willamette Sound represented by the Pleis- tocene dots. The islands of that grantl body of water as shown on the map are largely the Miocene hills, as Chehalem, the Eola Hills, the Waldo Hills, and the Buttes of Linn and Lane counties. Perhaps at times the lowest of these hills were covered by the waters of the Sound. Lindgren tells us Baker Val- ley, too, was a lake during this Pleistocene age. He believes the valley is the result of a fault at the eastern border of the Elkhorn mountains. If you turn to the map you will find the elevated beaches described in the Two Islands indicated by a Pleistocene border along the whole coast line of Oregon. As will be seen by the map the lakes in Oregon were very much larger then than now.

A portion of southeastern Oregon is of peculiar interest as belonging to the northern part of the "Great Basin" of Western America. The Oregon section of this great basin lies approximately between Stein Mountain on the east and Walker Range on the west, while the most northern portion of its boundary reaches Strawberry Range near Canyon.

The Great Basin is an area with no outer drainage and any excess of moisture which falls is soon evaporated into the dry atmosphere, so that its lakes rarely overflow and offer during tlie summer months become changed into dry alkali flats or playas.

Riissell tells us that the boundary line of the Oregon portion of the Great Basin is changeable. For .example the Klaipath basin used to be covered in the Pleistocene times by a long, narrow lake, "Probably including Klamath Marsh, Upper and Lower Klamath Lakes and Rhett Lake with much of their adjacent shores," and as this lake has an outlet the whole Klamath basin be- longed to the Great Basin structure which then extended to the Cascade mountains. But during some wet season this lake filled its basin and a trick- ling stream began wearing an outlet, first as a small brook then a larger stream, it finally grew into the Klamath river, with force enough to cut its way through the moimtains to the sea.

On the other hand we are told that during the Pleistocene the Malheur and Harney Basin was filled with a great lake which was drained by the Malheur river, but a later outflow of molten lava ran across the outlet form- ing a dam of volcanic rock through which it can not break and over which it can not flow. Thus, having no outlet, Harney and Malheur Lakes and Basins are now added to the Oregon section of the Great Basin.

Since so much has been written of faults in connection with the cause of the earthquake in California we may find fresh interest in studying the faults so common in this portion of Oregon.

Russell tells us this region has been cracked and broken by faults into long, narrow blocks running nearly north and south. Some of these "Oro- graphic Blocks" have been pushed up, others dropped down, but most of them have been tilted up on edge, the top of the block forming a gentle slope away from the uplifted side. A fine example of this "Block Mountain" type is found in Stein mountain in southei'n Harney county. Its precipitous eastern face stands five or six thousand feet above Alvord lake and valley at its base. This lake is deepest next the face of the precipice for the Alvord valley itself