LIVERMORE -- A large swath of vegetation kept short because of livestock grazing on grass helped slow a fire that burned 20 acres near Highway 84 in Livermore on Wednesday, an Alameda County fire official said.

Crews were called to the blaze along Vallecitos Road at 5:32 p.m. and had it extinguished within a half-hour, interim Fire Chief Dave Rocha said. The fire started along the highway and moved up a slope near the Livermore and Pleasanton border in unincorporated Alameda County.

The fire threatened a home atop the hill, and cell phone communication towers also were in harm's way for a brief time, but a quick response by crews from Alameda County Fire, Cal Fire and the Livermore-Pleasanton fire department prevented any property from being damaged, Rocha said.

Vegetation near the home had been cropped by livestock, and in that area flames moved slowly and were no more than a foot off the ground, Rocha said. Nobody was injured in the blaze, he said and no livestock was threatened.

The cause of the fire remains under investigation.

Staff writer Katie Nelson contributed to this report. Contact Rick Hurd at 925-945-4789 and follow him at Twitter.com/3rdERH.