Sen. Mark Udall's brother missing

Randy Udall, 61, of Carbondale, Colo., is a renewable energy and environmental advocate.

He has been an active voice urging caution on hydraulic fracturing, or fracking, the controversial drilling method that has led to a domestic oil-and-gas boom but brought fears of pollution.

He has testified before the Colorado Oil and Gas Conservation Commission on how far to set oil-and-gas wells back from homes during fracking.

Colorado has embraced the practice. Its Democratic governor, John Hickenlooper, has threatened to sue towns that ban fracking, and he’s testified on Capitol Hill in support of letting states regulate the process.