Among the more spectacular bloopers from Google.

All the roads and trails over the High Sierras are still buried under many feet of snow in May. They try to plow some major routes open for Memorial Day (which is an end-of-May vacation weekend and traditionally marks the beginnig of summer fun for many Americans), but it isn't always feasible.

You might be surprised by how deep the snowpack gets.

There are probably some youtube.com videos that would give an idea.

Also, it can be misleading when most of California is having warm, mild, summer-like weather in May -- and despite California's popular image and reputation for pleasant weather conditions -- it can still be mighty cold and challenging above seven thousand feet. I've been caught in late snowstorms and very cold rain and wild, driving windstorms in May in the Sierras. Without proper gear, much greater unpleasantnesses would certainly have been on tap.

And Death Valley is no joke either. It has the hottest temperature on record in the entire world (56.7 degrees C., or 134.1 F.), and has more days above 120 degrees than anywhere else. The sun is intense in May, and heat exhaustion and other exposure problems are real concerns.

This is not meant to be discouraging -- just encouraging you to know more about what you might be riding into, and to be prepared for it.