NORTH COAST, Calif. – State fire officials said Friday that 28 fires believed to have been sparked by lightning earlier this week have been fully contained.

Cal Fire said the wildland fires, located on the Sonoma-Lake-Napa Unit, included three in Lake County, 20 in Sonoma County, four in Solano County and one in Colusa County.

The wildland fires were reported beginning this past Monday morning through late afternoon Wednesday, Cal Fire said. They ranged in size from a single tree to four acres.

An estimated 8,000 lightning strikes started dozens of wildland fires across Northern California in that time period, according to Cal Fire.

The fires on the Sonoma-Lake-Napa Unit did not damage any homes or outbuildings, Cal Fire said, and no injuries were reported. Cal Fire said it is investigating each of the fires to rule out possible causes other than lightning.

In the region, there is a possibility of more fires, as the weather warms and smoldering lightning wildland fires “come to life,” Cal Fire said.

The agency said its resources are monitoring the areas which had fire activity and are ready to respond if new wildland fires occur.