The women "died of homicidal violence," said sheriff's spokesman Rich Niebusch, who would not elaborate on the cause of death, other than to say there were obvious signs of trauma.
He said authorities did not immediately have any suspects.
The women - one in her 20s and one in her 40s - were last seen alive by a witness who reported seeing them at the trailhead about 10 a.m. Tuesday, he said.
Sources speaking on a condition of anonymity said that the victims were mother and daughter.
The bodies were found by another hiker about three miles up the trail, which heads to Pinnacle Lake, south of Verlot. That person hiked out to notify authorities about 2:30 p.m. Tuesday, leaving a window of less than 4½ hours for the killings to have occurred, Niebusch said.
Niebusch said his department had been in contact with people investigators believe are relatives. He said investigators were confident the victims were from the Puget Sound area, but their names would be released by the medical examiner's office.
A man who answered the phone at the medical examiner's office but who would not give his name said autopsies would not be conducted before Thursday.
Investigators completed their work at the scene Wednesday, and carried the bodies out to the nearest road by foot, as bad weather prevented use of a helicopter.
In addition to autopsies, the next step would be to examine a Dodge Caravan, believed to belong to one of the victims, that was found at the trailhead, Niebusch said. He said that would be done Thursday.
He would not discuss any other evidence that might have been found.
Niebusch asked anyone with information, including people who might have been in the area Tuesday, to contact sheriff's officers at 425-388-3845.