A fire that sparked Friday afternoon in Mariposa County has forced immediate evacuations for nearby residents and is threatening thousands of homes, officials said. The state's fire agency said the fire activity is "extreme with frequent runs, spot fires and group torching." The Oak Fire started sometime after 2:30 p.m. near Highway 140 and Carstens Road by the community of Midpines, which is about 75 miles east of Modesto. Highway 140 is one of the main roads drivers use from the Central Coast to travel into Yosemite Valley. Subscribe to KCRA on YouTube now for more: http://bit.ly/1kjRAAn Get more Sacramento news: http://www.kcra.com Like us: http://facebook.com/KCRA3 Follow us: http://twitter.com/kcranews Instagram: https://www.instagram.com/kcranews/