Ancient fossil footprints have been stolen from Death Valley National Park.
The park announced Tuesday that scientists who visit the area to document the fossilized animal tracks discovered the theft recently and reported it to rangers.
The park says backpackers were photographed in the area and may have witnessed the theft or have information about it. The agency tweeted photos of the men in an effort to contact them.
A $1,000 reward is being offered by National Park Service investigators for information leading to an arrest and conviction.
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The fossils formed 3 million to 5 million years ago after animals walked across what was once a muddy lakeshore in the park that sprawls across 3.4 million acres in California and Nevada.
Park Superintendent Mike Reynolds says it's illegal to collect fossils, rocks or anything else in national parks.