The Valley Fire has destroyed at least 1,200 homes and killed three people since it started Sept. 12. It is the third most destructive fire in California history based on structures destroyed.
The declaration issued Tuesday releases federal money for recovery and cleanup.
Residents can apply for grants for home repairs and temporary housing as well as apply for low-cost loans for uninsured property.
The Lake County sheriff said Tuesday a search continues for two men reported missing. They are 61-year-old Robert Litchman of Middletown and 66-year-old Robert Fletcher of Cobb.
Funds approved for road repairs
The Federal Highway Administration Tuesday announced it is providing $2 million in federal emergency relief funds to Caltrans.
The money is to help repair roads, bridges, signs and guardrails damaged by the Valley Fire in Lake and Napa counties.
The Federal Highway Administration says the preliminary estimate of damage to roads and bridges from the Valley Fire is about $19 million.
Highways damaged by the wildfire include: SR-29, closed from Calistoga to the Napa/Lake County Line and from north of Hidden Valley Lake to SR-53; and SR-175, closed from Middletown to SR-29 near Clear Lake.
The FHWA's Emergency Relief program provides funding for highways and bridges damaged by natural disasters or catastrophic events.
The money will also be spent on work to re-stabilize slopes and embankments on certain highway sections.
The Associated Press contributed to this report.