Question: What is the county in which Sierra-at-Tahoe is located?

Context paragraphs:
Sierra-at-Tahoe: Sierra-at-Tahoe is a ski and snowboard resort in Twin Bridges, California south of Lake Tahoe.  Sierra-at-Tahoe is approximately 16 miles (26 km) south of Stateline, Nevada and 12 miles south of South Lake Tahoe on U.S. Route 50 and is contained within the Eldorado National Forest.  Sierra-at-Tahoe (often shortened to "Sierra") is a medium sized ski area in the Lake Tahoe region, and is well known for being a more family oriented resort and also having a high annual snowfall.  Sierra-at-Tahoe's terrain is 25 percent beginner, 50 percent Intermediate, and 25 percent advanced.

Twin Bridges, California: Twin Bridges is a small unincorporated community on U.S. Route 50 near the Desolation Wilderness in El Dorado County, California.  It is located 5 mi west of Echo Summit, at an elevation of 6115 ft .  It has a population of 14 people according to census figures, however, as of 2008 the road sign lists the population at 10.  Right after the town, the U.S. 50 eastbound starts a steep ascent to Echo Summit passing Sierra-at-Tahoe ski resort shortly before the summit.

Phillips, California: Phillips (formerly, Phillip's and Vade Post Office) is a small unincorporated community in El Dorado County, California.  It is located on the South Fork of the American River, 2.5 mi west of Echo Summit, at an elevation of 6,873 feet (2095 m).  It is the site of the Sierra-at-Tahoe ski resort.  The ZIP code is 95720.  The community is inside area code 530.

Stateline, Nevada: Stateline is a census-designated place (CDP) on the east shore of Lake Tahoe in Douglas County, Nevada, United States.  The population was 842 at the 2010 census.  The population swells considerably during the busy winter and summer seasons, due to the high number of hotel rooms and rental accommodations available.

Supporting paragraphs: Sierra-at-Tahoe Stateline, Nevada
Answer: Douglas County