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Federal jurisdiction over those washes hasn’t been questioned since Rosemont Copper first announced its plans to build the $1.5 billion project a decade ago. The company, now owned by Toronto-based Hudbay Minerals Inc., applied for a Clean Water Act permit for the project back in 2011 and announced its intention to apply in 2008.

A Rosemont consultant, in fact, developed a preliminary version of a formal determination document showing which washes on the mine site would be covered by Clean Water Act oversight years ago.

But the broader issue of federal control over development along mostly dry washes such as these has been subject of national legal disputes for years. Experts say Rosemont’s fate could be affected by how those disputes play out in the incoming administration of President-elect Donald Trump.

In a Nov. 17 letter to the Corps, Patrick Merrin, a top Hudbay official, wrote, “In our view, there is significant uncertainty as to whether the Corps has jurisdiction over the onsite drainages. In the event of an adverse final decision on our application, we anticipate that jurisdictional arguments will be a key element of our appeal ... .�

The Corps’ lower-level Los Angeles-based office has recommended denial of Rosemont’s permit. A decision will be made by the agency’s San Francisco-based South Pacific Division, which oversees the Los Angeles office. If that decision goes against Rosemont, the mining company legally can appeal to higher-level Corps officials who would make a final decision.

The Star obtained Merrin’s letter last week under the U.S. Freedom of Information Act, along with a letter from South Pacific Division Commander Col. Pete Helmlinger laying out some of the reason for the L.A. office’s recommendation. Hudbay didn’t respond to questions about this issue from the Star.

The Rosemont permit application seeks permission to dredge and put fill material such as mine waste rock and tailings in several ephemeral washes, which carry water only during storms.

The feds’ authority over many desert washes in the ÃÛèÖÖ±²¥ area has been clear since 2008, when the U.S. government declared the Santa Cruz River a legally navigable river even though most of it also runs only during storms. Under the Corps’ and EPA’s interpretation of court rulings, dry washes that are significant tributaries to a navigable river are legally covered by Clean Water Act rules. That means permits are needed for anyone wishing to significantly alter or otherwise impact the washes.

A highly controversial 2015 federal rule known as the “Waters of the U.S.� rule would have formally inscribed that practice onto the books. The phrase “waters of the U.S.� is used legally to describe rivers and washes that are covered by federal regulation.

But shortly after the EPA and Corps adopted the rule, many states including ÃÛèÖÖ±²¥ successfully stalled it in court until full-blown arguments can be heard over whether it’s legally authorized by the Clean Water Act.

Trump himself argued strongly against the “Waters of the U.S.� rule in his campaign as an example of federal overreach. He has called it extreme and unconstitutional and vows on his transition website to eliminate it.

Oklahoma Attorney General Scott Pruitt, Trump’s pick to run the EPA, is one of 30 attorneys general who has filed suit against the rule. He and other critics say it violates private property rights and expands federal authority.

The EPA and environmentalists say the rule gives needed protection to clean water and washes that serve important biological functions and feed major rivers.