Colorado has passed its first voter-mandated reintroduction of endangered wolves in U.S. history. On Monday, Dec. 18, the mandate became a reality as the first gray wolf released on Colorado soil dashed out of a metal crate and into the Grand County mountains. Four other wolves soon followed.

Wildlife officials worked from dusk until dawn to capture the five wolves Sunday, Dec. 17, in Oregon. Two teams used planes to look for wolf tracks and analyze data from wolf collars.

Once teams in helicopters shot the wolves with tranquilizer, veterinarians and biologists checked their health, took blood and tissue samples, and equipped the wolves with radio collars.

Colorado wildlife officials said the wolves came from five packs in Oregon. The officials did not disclose the exact location for safety purposes, but the location is confirmed to be in the north-central mountains.