WARM SPRINGS, Ore. (AP) — A small private business jet crashed in mountainous terrain in the Warm Springs Indian Reservation of central Oregon, killing the pilot and a single passenger on board, authorities said Sunday.

Warm Springs tribal police were notified by air traffic controllers in Seattle, Washington at about 2:30 p.m. PST Saturday of a possible crash in the Mutton Mountains on the reservation, roughly 20 miles (32 kilometers) north of Warm Springs, said tribal police Lt. Ron Gregory.

Flyovers by the Oregon State Police and the U.S. Air Force confirmed a crash late Saturday. But snow, mud, downed trees and rugged terrain prevented rescuers from Warm Springs police, Wasco County and state police from reaching the remote site until about 12 p.m. Sunday, Gregory said.

Rescuers confirmed that the pilot and a lone passenger on the twin-engine Cessna Citation C560 were killed, Gregory said.

The victims’ identities weren’t immediately released, and details on the flight’s itinerary and the owner of the aircraft weren’t immediately available.

The National Transportation Safety Board was investigating the crash, said NTSB spokesman Chris O’Neil.