Wildfires burning near Northern California vineyards and in the Yosemite National Park area were threatening hundreds of homes even as crews worked to contain them.

A wildfire in northern California is threatening more than 500 homes this morning.

The Sand Fire in the Sierra Nevada foothills east of Sacramento was 50 percent surrounded as of late Sunday, after burning 13 homes and 38 outbuildings. It has scorched roughly six square miles of rugged grassland and timber near wine-growing regions in Amador and El Dorado Counties.7

In spite of establishing a firebreak perimeter on the ground and hitting their targets from the air, 1,900 firefighters have been unable to bring this wildfire under control, due to the steep, rugged foothills of the Sierra Nevada, combined with 100-degree heat, strong winds and drought-dry brush.

“During the day we have up-canyon winds because the heat is rising,” California Fire Public Information Officer Brice Bennett told CBS News. “And during the night we have down-canyon winds. The fire actually changes direction.”