Several Elmore County roads in the Anderson Ranch Reservoir area are closed due to mudslides.
Boise National Forest officials on Friday morning were conducting a helicopter survey of the damage.
Boise National Forest spokesman David Olson said the House Mountain area received one inch of rain late Thursday, which flowed across an intensely burned area of Elk Complex fire causing flooding in some drainages.
A Granite Creek mudflow crossed the South Fork Boise River Road and dumped into the river, possibly causing some kind of blockage on the South Fork. A downstream river gauge at Neal bridge typically records about 600 cfs, said Olson. Overnight, the gauge dropped to about 250 cfs and then increased to 650 cfs flow, indicating some sort of temporary blockage.
Above Anderson Ranch Dam, mudflows are reported on Evans and Castle creeks.
Fall Creek Road is closed with reports of large boulders on the roadway.
More rain is expected in the area on Friday. The National Weather Service has issued a flash flood watch for the central Idaho mountains effective from 2 to 11 p.m. Friday.