It will be some time before investigators know what caused the crash Monday night of a Utah National Guard Apache helicopter that killed two pilots who were on a training mission at the time.

"In the meantime, we're going to take care of the families as best we can," Guard spokesman Maj. Hank McIntire said about the families of both pilots.

Standard procedure is that the names of the pilots will be withheld for 24 hours after their families have been notified of the crash. McIntire said the families of the two men, both Utahns, were notified late last night after the approximately 8 p.m. crash in the mountains west of Utah Lake. A casualty assistance officer has been assigned to each family.

The pilots were both veterans of Operation Enduring Freedom and had served in Afghanistan with the First Battalion, 211th Aviation, in 2004-2005.

All of the Utah Guard's AH-64 Apaches and Blackhawk helicopters have been indefinitely grounded as a result of the crash.

"As a safety precaution, you ground your aircraft and make sure all of the safety procedures continue to be followed," McIntire said.

A team from the U.S. Army Aviation Safety Center at Fort Rucker in Alabama will be leading the investigation into the cause of the fatal crash. It's unknown when the craft, which looks "fairly intact," according to McIntire, will be removed from the site. He said there was no ordnance on board at the time and that there didn't appear to be any fire or explosion.

It's also unclear exactly how word of the crash reached responders. McIntire said he had not heard that there was any radio distress call from either pilot.

Utah County Sheriff spokesman Spencer Cannon said the pilots were overdue, which prompted a search by Guard members into what he said was an "isolated" area with probably few, if any, eyewitnesses.

A medical helicopter responded to the site, but both men were declared dead at the scene. Weather, he added, does not appear to have been a factor in the crash.

Apache and Blackhawk pilots with the Utah Guard have experienced hard landings in the past, but McIntire said Tuesday he could not recall a single crash in the Utah Guard's history of "this magnitude."

Maj. Gen. Brian Tarbet issued a statement Tuesday, saying he was "deeply saddened" by the loss of two veteran pilots.

"Our thoughts and prayers are with their families at this difficult time," he said. "We as a Guard family pledge all we can do to assist and comfort them as we share in their loss."

A press conference in Draper with the general is expected at 1 p.m. today.

Contributing: Sara Israelsen