The Oak Fire started Friday afternoon southwest of the park near the town of Midpines in Mariposa County and by Saturday had grown to nearly 19 square miles (48 square kilometers), according to the California Department of Forestry and Fire Protection, or Cal Fire. It erupted as firefighters made progress against an earlier blaze that burned to the edge of a grove of giant sequoias in the southernmost part of Yosemite park. Evacuation orders were put in effect Saturday for over 6,000 people living across a several-mile span in the sparsely populated, rural area, said Daniel Patterson, a spokesman for the Sierra National Forest.