"The creation of these huge monuments has unnecessarily had significant and negative impacts upon the traditional uses of these lands and upon the lives and livelihoods of the local populations that have stewarded the lands for generations," said Clarke, who was BLM head under former President George W. Bush.
Clarke's testimony doesn't square with two studies on the issue. One by Headwaters Economics concluded that designation of the Grand Staircase did not significantly change economic growth trends seen in surrounding areas, with rising population, jobs and per capita income. Another study, by Utah State University, found that the Grand Staircase declaration had little or no effect on host counties' economic situation.
The testimony comes as Interior Secretary Ryan Zinke, as ordered by President Donald Trump, is reviewing the Bears Ears and Grand Staircase designations and other national monuments named in the past 21 years. Zinke must report back recommendations by June 10 on Bears Ears and the rest within four months.
Rep. Rob Bishop, a Utah Republican who heads the Natural Resources Committee, charged that the Bears Ears designation ignored the wishes of residents, especially Native Americans in the area.
"Never in my 14 years of Congress have I seen such a concerted effort to suppress the voices of local tribes by such powerful, deep-pocketed opponents," Bishop said. "No local tribe in San Juan County, Utah, where the national monument is located, supported this designation. But most do not know this, because it is barely reported."
Obama's designation had the support of the Bears Ears Inter-Tribal Coalition, a coalition of five sovereign Tribal Nations: Hopi, Navajo, Ute Indian Tribe, Ute Mountain Ute and Zuni.
Rep. Raul Grijalva of Arizona, the top Democrat on the Natural Resources Committee, countered the GOP's complaints about the 1906 Antiquities Act, noting that presidents since Teddy Roosevelt have used it to preserve and protect landscapes across America.
"You can't find a more popular government program," Grijalva said. "And yet we're here today because my colleagues in the majority want to destroy the law and potentially even abolish existing national monuments."
He noted last week's Outdoor Industry Association report that outdoor recreation supports 7.6 million jobs and provides $887 billion in consumer spending.
"If the only monuments Donald Trump wants are hotels, so be it," Grijalva added. "But the national monuments established by his predecessors are not subject to Donald Trump's whims."
More than 450 organizations, ranging from the American Bird Conservancy to the Wyoming Outdoor Council, signed a letter unveiled Tuesday opposing any effort to reduce or rescind national monuments.
"Our national monuments protect our uniquely American heritage and we stand with the overwhelming majority of our fellow Americans in defending them from efforts to undermine protections for parks and monuments," the groups wrote in the open letter. "We urge you to refrain from any effort to shrink, repeal or otherwise undermine any national monuments."