Distance: 7.2 miles (11.6 km) round trip from Yosemite Valley;
8.2 miles (13.2 km) round trip from Porcupine Creek (Tioga Road);
10.0 miles (16 km) round trip from Snow Creek trailhead (Tioga Road)
Tioga Road Trailhead Elevations: 8,100 feet (2,470 meters) at Porcupine Creek, 8,500 feet (2,590 meters) at Snow Creek trailhead
Yosemite Valley Elevation: 4,000 feet (1,220 meters)
Total Elevation Gain: 2,700 feet (820 meters) from Yosemite Valley;
1,300 feet (400 meters) descent from Porcupine Flat; 1,700 feet (520 meters) descent from Snow Creek trailhead
The red line marks the Tenaya Creek Canyon loop trail, which passes Mirror Lake and returns to Yosemite Valley. It's relatively flat and easy, and you can take either the north or south sides to reach the Snow Creek trail proper, though the south side is periodically closed by rockslides. Hike that stretch when it's open and you'll be able to readily pick out the trouble spot no matter what grades you got in Earth Science. It may have been just timing or coincidence, but I've encountered much higher concentrations of mosquitoes on the southern half of the loop.
The blue line marks the infamous stretch of the Snow Creek Trail that switchbacks its way from the valley floor up to the rim. It's surprising how much pain can be packed into such a tiny little squiggly line.
The purple line shows the Snow Creek Trail's more civilized side, meandering from the rim to the Tioga Road. Even though it has 1,700 feet of vertical in its 5-mile route, it's far easier than the trek up the rim.
The yellow line shows the shorter alternate route via the North Dome trailhead. The sharp turn to the east a mile and a half along is where the trail forks.