U.S. Sens. Patty Murray and Maria Cantwell said in a letter to Ryan Zinke, U.S. secretary of the interior, that they oppose any attempt to modify the Hanford Reach National Monument designation.

The Washington Democrats told the Trump appointee in a May 10 letter that the Hanford Reach should be preserved as it is. They called the 200,000-acre monument a local, state and national treasure well worth protecting.

The Department of Interior is reviewing national monuments established in the past 21 years after an April 26 executive order signed by President Donald Trump.

The review covers 21 national monuments in the West and could lead to alterations or outright removal of the designations. President Bill Clinton established the Hanford Reach monument in 2000.

Murray and Cantwell, both Democrats, reminded Zinke that he called himself a Theodore Roosevelt conservationist in public and private conversations during his confirmation process.

“Rolling back protections for some of our nation’s most prized public spaces, like the Hanford Reach National Monument, does not exemplify President (Theodore) Roosevelt,” the senators wrote.

The Hanford Reach covers a large swath of land in Southeast Washington and is home to the last 51-mile, free-flowing stretch of the Columbia River.

It is managed by the U.S. Fish and Wildlife Services and is home to 43 species of fish, 42 mammal species and 258 bird species and is an important cultural resource to the Confederated Tribes and Bands of the Yakama Nation, Confederated Tribes of the Colville Reservation, Nez Perce Tribe, Confederated Tribes of the Umatilla Indian Reservation and the Wanapum Band of Priest Rapids.

Some areas of the Reach are open to the public for hiking, boating, fishing, hunting and other recreational activities. It is part of an outdoor recreational economy that generates $22.5 billion in consumer spending in Washington, they wrote.

The Hanford Reach National Monument is distinct from the Manhattan Project National Park, a multisite park established in 2015 to honor the top-secret efforts to design, test and build the world’s first atomic weapons. It includes facilities at Los Alamos, New Mexico, Oak Ridge, Tennessee, and the Hanford Nuclear Reservation.

The Manhattan Project played a major role in preserving the Hanford Reach from development. The safety perimeter around the Hanford reservation ensured the lands were largely untouched beginning in the early 1940s.