YAKIMA — A rock slab from a ridge in south-central Washington is continuing to slide, but the rate of its descent has slowed over time, officials said.

A section of Rattlesnake Ridge continues to slide at a rate of 2 to 3 inches per week, The Yakima Herald-Republic reports.

State and county officials and scientists began monitoring the slide in October 2017 when a crack was spotted in the ridge near Union Gap, about 4 miles south of Yakima.

Horace Ward of the Yakima Valley Office of Emergency Management said the latest sensor network readings indicate the slowest point of the 200-foot-deep slide is moving about 0.15 feet (0.05 meters) per week.

Washington State DNR uses a drone to map ground movement and speed of the Rattlesnake Ridge landslide. (Courtesy of Washington State DNR)

The fastest slide area is moving about 3 inches weekly, Ward said.

Stephen Reidel, a Washington State University adjunct geology professor, said the slide is likely to halt before reaching Interstate 82 or the Yakima River.

Rocks from the slide falling into the Columbia Asphalt quarry are likely to form a buttress that will stop its advance, Reidel said.

“If you just take a look at it, the rocks fall down the hill to the quarry,” Reidel said. “It is as far as it is going.”