Nevada authorities say driver fatigue is a possible cause of a deadly crash of a mountain resort's shuttle bus in California's Sierra Nevada.

California Highway Patrol Officer Steve Skeen said Sunday that investigators also are focusing on whether the driver had a medical condition that contributed to the accident Saturday that killed one passenger and injured 24 others. All the bus passengers were resort employees.

The bus, operated by the Resort at Squaw Creek just north of Lake Tahoe, veered off the freeway, struck a guardrail and rolled at least once before stopping in a ditch about 20 miles west of Reno.

Skeen says 11 people remained hospitalized Sunday. One was listed in critical condition.