Pacific Gas & Electric spokesman JD Guidi said the outage was reported at approximately 7:21 p.m. Sunday.
He said the area affected stretched north of Middletown along Highway 29, and along the Butts Canyon Road to the Napa County line.
Also affected were Cobb, a small area of Kelseyville and one resident who reported losing power in Clearlake Park, Guidi said.
Guidi said 975 customers were impacted in Cobb, 63 in Kelseyville, one in Clearlake Park and 1,376 in Middletown.
By around 10:30 p.m. approximately 674 Middletown customers had their power restored, he said.
Guidi said the cause was still under investigation, with PG&E crews working as quickly and safely as possible to get power restored.
He said power was expected to be restored to the remaining 1,322 customers at around 6 a.m. Monday.
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