Mariposa is on Highway 49, the Gold Country spine road, and on Highway 140, which runs east through the Merced River Canyon to Yosemite Valley. The nearest major airports are Fresno Yosemite International (about 65 miles south) and Merced Regional (about 40 miles west on Highway 140). San Francisco is roughly three hours by car via Highway 99 or I-580.
There is no public transport directly to Mariposa. YARTS (Yosemite Area Regional Transportation System) runs buses from Merced along Highway 140 through Mariposa to Yosemite Valley, which makes it possible to reach the park without a car; check yarts.com for schedules. Otherwise a car is essential for getting around the area.