Updated

A fallen power line caused a South Dakota wildfire that has become the third-largest ever recorded in the Black Hills, Custer State Park officials said Thursday.

The blaze was 50 percent contained, up from 10 percent reported previously, and the park said in a statement that fire crews are making gains as mop up work starts within the fire's perimeter. The fire has consumed more than 73 square miles (190 square kilometers).

Custer State Park is a top South Dakota tourist destination just south of Mount Rushmore National Memorial in the southwest part of the state. Visitors often drive to see roaming buffalo, elk and bighorn sheep, and the park hosts a popular annual buffalo roundup. Officials are evaluating the fire's effects on park wildlife.

Spokeswoman Lydia Austin said the blaze didn't expand overnight past fire lines, which can be roads or strips where firefighters remove vegetation so there's nothing for the fire to burn.

Austin said that there had been no injuries, and no main park buildings were destroyed in the blaze. Efforts to protect the popular State Game Lodge and Blue Bell Lodge have been successful.

Light snow helped with the fire in the north, but conditions were dry within the perimeter, the park said in the statement. It is closed while officials evaluate public and staff safety.

The fire began Monday. The park said that the Fire Investigator's Office in the South Dakota Wildland Fire Division attributed the cause to a downed power line.