Travel from San Francisco area to Reno in March?

There's no way to predict that right now.

Highway 80 to Reno goes over Donner Pass (7056 feet), and California's rainy season includes the month of March.

Unless the dry spell of the last three weeks continues, there will probably be plenty of snow at Lake Tahoe. The road conditions, however, depend on whether there has been a recent storm. The major highways could be clear, or closed, or open only to vehicles with chains or four-wheel drive.

The elevation of Yosemite Valley is only 4000 feet; and if you travel on highway 140 (through Merced and Mariposa), you never go higher than that. Yosemite Valley might be free of snow in March, but it's certainly possible that a cold storm could dump snow on Yosemite Valley and the nearby section of highway 140.

It's always a good idea to carry chains if you travel to the mountains in March. At the very least, look up the current road conditions, and check the latest weather forecast before you leave.

California highway conditions are here:

http://www.dot.ca.gov/cgi-bin/roads.cgi

Current conditions for Yosemite are here:

http://www.nps.gov/yose/planyourvisit/conditions.h...

Note that Yosemite National Park is much bigger than Yosemite Valley. The Tioga Road across the park is closed for the winter (typically until late May). The Mariposa Grove may be accessible, but the hiking trails there will be covered with snow (and open to cross-country skiiers and snowshoers). The Valley, however, is often easily accessible in March, and that's a great time to see it without large crowds.

Finally, keep in mind that there is heavy traffic going to Tahoe on Friday afternoons/evenings, and returning late Sunday. If you can avoid these times, you'll have a more enjoyable drive.