The crash, involving a pickup into a ditch, occurred on the Dry Creek Cutoff near Middletown at around 6:20 p.m., according to radio reports.
The California Highway Patrol said one person was ejected from the pickup's bed while another person was trapped inside.
The names of those involved were not immediately available.
An air ambulance transported one subject to Santa Rosa Memorial Hospital and the CHP indicated the other subjects were transported to St. Helena Hospital, Clearlake.
The CHP reported a blood draw was ordered as part of the investigation.
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