Indian Peak Ranch is located roughly 16 miles (26 km) from Mariposa and 20 miles (32 km) from Oakhurst - see the blue balloon near the middle of the above map. It's 50 miles (80 km) from the ranch to Yosemite via Mariposa, and 35 miles (55 km) to the park's south entrance via Oakhurst.
If you're coming from Mariposa, take Highway 49 east to Hirsch Road (see the map below for a more zoomed-in version with road names visible). When Hirsch Road intersects with Indian Peak Road, turn left, and then turn right when Indian Peak intersects with Usona Road. From there, it's a little under 2 miles (3 km) to the ranch's entrance.
If you're arriving from Oakhurst, take Highway 49 west to Usona Road, and stay on it until it reaches the ranch a little under 7 miles (11 km) later. (When the road intersects with Indian Peak Road, it'll become Indian Peak Road, though you won't need to turn.)
The last half mile or so of the road is unpaved, and there's an additional brief unpaved stretch if you're taking the Oakhurst route, but you won't need an all-wheel-drive vehicle. The ranch's website has more detailed directions.