By following forest roads from Alturas to Bly you can connect to Oregon's O&C trail, and ride all the way to Klamath Falls.  There is bus service from K-Falls to Alturas to Susanville on the Sage Stage.  Not real convenient scheduling but is an option.
From the Bizz Trail terminus in Westwood you can ride the not yet completed Collins Pine railroad trail to Chester, and from Chester ride the paved Almanor Trail along the lakeshore to Canyon Dam.  Bus service from Chester to Susanville daily. 
All total about 300 miles of bike route with bus shuttling possible.

Of course, you can ride forest roads around the area for an infinite number of possible routes.  I have a route that circumnavigates Lassen Volcanic NP with forest roads and some bike legal singletrack.  I also penciled out a route from Mt Shasta to Lake Tahoe on forest roads.

Also a combo paddle/backpack/bike pack trip through and around LVNP.

All trails in Point Reyes are closed to bikes.  The roads are open to bikes.  Marin County is basically anti-bike and the National Park Service just follows local sentiment.

If you do not mind riding on unsurfaced forest roads you can create an infinite number of loops.  Many of the roads are gated or barricaded to motor vehicles, so you would have the road to yourself.  Get a forest visitor map and start laying out routes.  Use Google Earth to cross check your route for potential campsites, views, veg types, etc.  This goes for almost any National Forest land, not just Stanislaus.

Do you mean bicycling the Beartooth?  For roadies that is considered an epic ride.

As a general rule non-wilderness trails are open to mtb unless specifically closed.  The PCT is closed, although in many areas the FS and BLM are not actively enforcing the ban.  It is still illegal, so if by any chance you are cited on the PCT you will have to pay the fine.

Check the source of anyone who tells you trail XYZ is closed to bikes.  There are a lot of groups and websites that say a trail is closed, but really is open to bikes.  Call the local FS or BLM office and ask.  Do not take the word of some third party.
Whether it is ridable or not is a different matter...

Do not limit yourself to singletrack only. There are a lot of good routes you can string together using forest roads as connectors.

I have a tentative trip that involves a short paddle, three days backpacking across a Wilderness, then bikepacking back to the start.  I want to stash the bike just outside the Wilderness boundary.  I will lock it to a tree a good distance off the trail out of sight, and throw a camo tarp over it.  This particular trail gets a fair amount of use so I have reservations.

I  have done this once before, but the stash spot was well off the beaten track along a little used road, and was only for one night.  Has anyone hidden a bike for a few days like this?  Any problems?

Hmmm....

Has mike vandeman visited Colorado lately?

Retired from the feds in 2005 after 32 years.  Started a second career for local government, now looking forward to my 2nd pension.

Call LBS' along the route and see if they will hold the package for you.  They are usually open more hours than the local post office and may open the shop after hours if you call them.  Many shop owners are happy to oblige.  If the shop is not willing, they could recommend a local club or individual for you.

Many private RV parks will have a few tent only sites.  Usually $10-15 per night, but you have showers, laundry and amenities.

Mmmm...

May want to postpone that trip until the drug wars slow down a bit...  I am not sure I would want to be an American tourist on a bicycle...

'Bodfish' is his nickname.  Chuck Elliot owns Bodfish Bicycles in Chester.
The route was another book.

Please do.  I'd be interested in looking at it.

I read of the route in a book some years ago, since loaned out and lost.  I was unable to find an online description.  If memory serves, it started near McCloud, wandered on forest roads south, followed the 17 Road along the west side of Lassen Park, cut east to Lake Almanor area to Westwood, then Moonlight pass south through the east side of Plumas County, to Truckee, then Tahoe.  The area is very well roaded and many variations could be created.

A route I have pencilled out circumnavigates Lassen Park.  Another intriguing route is combining the Oregon OC&E trail K-Falls to Bly, south on forest roads to Alturas, then riding the Modoc Line Trail to Susanville, then the Bizz Johnson Trail to Westwood, then the yet undeveloped Collins Pine Trail to Chester.  All total over 300 miles mostly on Rails-to-Trail.  It is possible (not convenient) to put together a shuttle from Chester to K-Falls using public bus systems. 

There already is a route from Shasta to Tahoe.  Mostly forest roads, only a small amount of singletrack.  I'll look around and see if I can find a link.

Not sure what you are asking.

If you want to ride mostly forest roads there is an infinite number of loops and routes you could string together. 

There are not a lot of long (multi-day) singletracks in the Sierra.  Most of the suitable trails are locked up in designated Wilderness.  If you are willing to drive a bit you can tie together about 300 miles or so of Rails to Trail in NE CA and southern OR.

I have a friend living in Reno. Does anyone know about the riding there?

Reno is a university and ski town with casinos.  All the amenities.  Tahoe and Downieville are just a short hop away.  No winter riding.  Lots of dual track riding on the desert side, and you can dirt road ride to good single track from the Sierra side.  You are close to Cali without having to pay Cali taxes (NV is considered a low tax state with no income tax, Cali is the highest tax state).  so stay out of Cali except to visit.

Or the Yampa river trail

Motorcycles and ATVs also drive on forest roads, often faster than the highways.  Check with the local Forest Service office and explain your situation.  There may be some gated roads open to bikes.

Generally, the further from towns the less motorized traffic.  Also look for Level 2 or 3 roads -- lower maintenance level. These roads will often have a vertical sign post rather than the horizontal or trapezoidal signs that designate higher level roads.

Have you considered Yellowstone National Park?  For a few weeks in the Spring the Park roads are clear of snow, but are still closed to vehicles.  The roads are open to bikes during this period, and there is almost no road traffic (a few NPS and contractor vehicles).  The YNP website gives details.

I'm not fast.  :-(

You only have to be faster than one other person...

Solo is the only way to go.  Alone with your thoughts.  Setting your own pace and itinerary.  Changing your route in the middle without having to agree with a partner.  Plus the feeling of being more alive when you realize you are responsible for yourself with no safety net of a partner.

There is no increased risk of a mishap.  The risk is not having someone to help you if there is a mishap.  On the contrary, solo is safer for me.  I am more cautious and take fewer risks.

On other forums I have been criticized and ridiculed when I state I backpack off trail solo, often without an itinerary, deciding upon my route as I go.  But I am very comfortable solo.  I am confident in my skills as is my wife.  She does not worry about me on my 'me time'.  This does not mean I am blissfully ignorant or flippant of the risks,  I am very aware, and mitigate by taking the proper precautions.  I am in my comfort zone solo.

I thought PCT meant Perfect Cycling Trail!   

In seriousness, though, it is still a long time off.  The Forest Service has indicated it may be interested in investigating opening parts of the trail to bikes.  It is just in the talking stage now, no timeline yet.  The entire trail will never be opened as it passes through many Wilderness Areas and National Parks (opening those areas to bikes is another ongoing issue not to be resolved soon).  The various PCT organizations are staunchly opposed, of course.  Like any special interest group they resist any change from the status quo.  I am sure ol' Mike Vandeman is absolutely apoplectic over the proposal -- his anti-bike histrionics are legendary and sometimes rather amusing.

In some areas, the Forest Service has not been enforcing the current ban and largely ignoring bike use, save for the occasional knucklehead that abuses the trail and gives all bike riders a bad image.  So for the interim follow the current regulations and stay off the PCT, while actively trying to change the regulations.