SAN FRANCISCO (AP) -- Thousands of lightning strikes in Northern California are to blame for setting more than 800 wildfires in less than a day.

Fire crews from Nevada and Oregon are helping the state battle the fires set by the weekend storm. It brought little or no rain but plenty of sparks to California's parched forests and grasslands.

The storm was unusual not only because it generated so many lightning strikes over a large geographical area, but also because it struck so early in the season and moved in from the Pacific Ocean. Such storms usually don't arrive until late July or August and typically form southeast of California.

The lightning-caused fires have scorched tens of thousands of acres and forced hundreds of residents to flee their homes. Thousands of firefighters are still working to contain them.

And the state fire protection agency is urging the public to be very cautious due to the extreme dryness.