SAN FRANCISCO (CBS NEWS) -- The fate of thousands of wild horses hangs in the balance as the Senate considers an amendment to a spending bill that would allow euthanasia of mustangs and burros roaming free on land owned by the federal government.

The amendment would allow the Interior Department's Bureau of Land Management (BLM) to sell excess wild horses without an assurance they wouldn't be slaughtered. The matter will eventually be settled in negotiations between the Senate and the House.

CBS San Francisco traveled to the Utah desert, 50 miles northwest of Cedar City, to witness a federally mandated round-up of an icon of the American West.

Using a helicopter that looks like it was stolen from the set of M*A*S*H, federal agents began the process of gathering 50 wild horses.

"When you have horses that close, when they come into a trap site, they're very fresh, they have a lot of energy. When you're gathering wild horses, they are wild animals," said Gus Ward, the BLM's Wild Horse and Burro lead for Utah.

The roundup is the result of a lawsuit settled by the state of Utah over horses encroaching on ranch land. With repeated helicopter passes, stallions, mares and foals are driven out of hills and corralled into a trap to be sorted.

From there, they'll be taken to a holding facility and hopefully adopted.

The BLM is responsible for the wild horses. The agency says there should be about 200 horses on this stretch of land. But there are closer to 700. The BLM warns the horses are at risk for starvation in higher numbers.

Matthew Wood owns the ranch where the roundup happened.

"I enjoy seeing a horse or two now and then, but it falls into the same category as seeing a nice big bull elk or nice big mule deer or a bear or something like that. But when it gets to be so many of them that they're destroying their own habitat, they're not pretty anymore," said Wood.

The roundup can be hard to watch, as the terrified wild horses are driven out of the mountains by sounds emitted from a helicopter, forced up hillsides and down gullies and ultimately drawn into the corral by a so-called "Judas horse" that leads the way.

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