Originally Posted by Razel
Well, three passes, 120, 108, and 4 aren't generally open until after Memorial day (unofficial start of summer), so that part of NorCal is questionable. Not that they're essential, as 88, 89, 70 and some of the Nevada roads along U.S. 395 are great for riding. That's along the Sierra's. There's also 299, 199, 36, and 93 on the west side of I-5 that are great for spendind a couple of days during the week. Problem is, though, that during the weekdays, traffic is a bit higher due to all the kiddies being out of school after the middle of June, so you get a tight window of opportunity with some roads during the weekdays. Weekends? Eh...anywhere from worse to horribly worse.
Plans are in the works for a Sierra Rally in September, right around the 14th in Sonora, but details are still being worked out. Misses the vacationing hoardes in cages, campers, and motorhomes, yet the weather is still suitable for normal gear and the passes are still open.
Conditions are actually dry now but more snow is likely - most all roads are generally clear by the end of May - but some may still be closed like Razel says until Memorial day May 26.
Since you will probably be coming down from the north I highly recommend taking 44 east off 5 from Redding toward Lassen Volcano National Park. Follow 89 through the park through Quincy all the way to North Shore Lake Tahoe. There are several side trips you can take to view some pristine mountain lakes along the way.
This is the road less travelled and I have never experienced any traffic issues that you can't blow past. You will encounter well over 100 miles of great twisties, some really nice small towns and awesome scenery.
From North Shore Lake Tahoe, ride around the west side of Lake Tahoe and once you reach South Lake you'll have multiple options, the 3 passes mentioned above are all great rides.
Sand typically isn't an issue but as always in the mountins beware of the occasional sand but more common sticks and rocks.