MOUNT VERNON  (AP) — A Seattle art dealer says a large mural originally mistaken for a tarp is an original 1941 painting from Northwest School artist William Cumming.

The mural, painted on canvas measuring 28 feet long and 7 feet tall, had collected dust for decades in barns belonging to Tony Breckenridge’s family.

Art gallery owner John Braseth told the Skagit Valley Herald the painting is worth at least $100,000. He says it’s a priceless piece of Skagit County and state history.

Cumming was part of the Northwest School of art, a movement of the 1930s and 40s with roots in Skagit County.

Breckenridge initially thought the painting was from a junior livestock show and offered it up to the Skagit County Fair in Mount Vernon, where it was displayed this month.