Great Basin

The board marks a boundary the basin has not always kept. In the Ice Ages the lakes here rose until they spilled east through Malheur Gap into the Malheur River, and the Harney Basin drained by the Snake and the Columbia to the sea the board says its water never reaches. The Voltage lava flow dammed the gap, in place by about 32,000 years ago, and closed the basin. Even since, geologists allow that the lake may have topped the gap again in the wettest centuries, and in very wet years it still spreads across the valley floor.

What the plaque says

Great Basin This site marks the northern limit of the Great Basin, a region some six hundred miles long and up to five hundred miles wide. It began forming 17 million years ago as the result of regional uplift and east-west stretching by geologic forces that continue today. This stretching created a pattern of north-trending mountain ranges separated by broad flat valleys. Precipitation that falls within the Great Basin leaves only by evaporation, with no outlet to the sea. During the Ice Ages. Small lakes in the valleys expanded to cover thousands of square miles.

Where it stands

More markers nearby

• The Terrible Trail — 10.0 mi
• American Indian Seasonal Round — 30 mi