Mariposa is a great place to stay if you are interested in exploring the Merced River. In summer the Merced River is a great place to swim as well as go white water rafting. The American River Recreation, ARTA River Trips, OARS, Whitewater Excitement, and Zephyr Whitewater are several white water rafting companies in Mariposa. They will provide you with everything you need for a great river adventure. Just make sure you call ahead of time to see if the water levels are good for this activity.
Blue Heron sports, 5081 Highway 140, ☎ (209) 742-2300. Nice little outdoor shop for trekking, camping, fishing and outdoor activities. Owner is very friendly and has excellent tips on planning the yosemite trip.edit