GROVELAND (AP) — Unnaturally long intervals between wildfires and years of drought primed the Sierra Nevada for the explosive conflagration chewing up the rugged landscape on the edge of Yosemite National Park, forestry experts say. The fire had ravaged 282 square miles by Tuesday, the biggest in the Sierra's recorded history and one of the largest on record in California. Containment increased to 20 percent but the number of destroyed structures rose to 101 and some 4,500 structures remained threatened.