On Monday, the 1,000th California red-legged frog raised at the San Francisco Zoo was released into Yosemite National Park as part of a program aimed at reintroducing the nearly-extinct amphibian into areas where it has not been seen for 50 years.

San Francisco Zoo and Gardens

Yosemite National Park saw the California red-legged frog vanish in large part because of the introduction of the non-native bullfrog.

The milestone release came after three years of collaboration between several agencies including the San Francisco Zoological Society, who raised the frogs from eggs and tadpoles, and the National Park Service. Other agencies that were part of the effort were Yosemite Conservancy, U.S. Fish and Wildlife Service and the California Department of Fish and Wildlife.