Wahluke Slope

It is a broad, south-facing slope with a grade of about 8%,[1] situated between the Saddle Mountains and the Columbia River's Hanford Reach.

It has been described as "basically a 13-mile-wide gravel bar" created by the Glacial Lake Missoula floods at the end of the last ice age about 15,000 years ago.

[4][5] The land was acquired by the U.S. government for the Hanford Nuclear Reservation and the residents, including Wanapum people, ordered to leave in 1943.

[6] In two actions in 1953 and 1958 the Atomic Energy Commission returned almost 200,000 acres (810 km2) to public use, mostly for agriculture with irrigation recently provided by Columbia Basin Project sources.

[7] Settlement on the Slope by non-Native Americans has been termed as troubled, initially due to lack of water, then later by the Federal Government's land policies, resulting in "sporadic" growth of the town of Mattawa.