My dad's 60th birthday is coming up, and we'd like to go away for the
weekend - somewhere within a few hours driving distance of San
Francisco.

He loves to fish, so I'd like to know a few decent RIVER fishing spots
where we might be able to rent a place for the weekend.

This research question focuses on the FISHING - I can figure out the
lodging (or, pay you additional to do so).

Essentially, I'd like to know a few spots that are good for river
fishing during April/May/June.  Within 3-4 hours driving from San
Francisco, CA.

If online is not a good resource, feel free to point out any books
that I might find in the local bookstore.

Thanks!

There is fishing and fishing.  If he is fly fisherman, his
requirements may be different.  If you know anything about his
preferences for type of fishing or fish, please let us know with a
clarification.

You will find loads of sites with a search for:  northern california fishing

You could look at the nearest to San Francisco, the Russian River:
http://www.fishsniffer.com/maps/russianriver.html
http://www.russianrivertravel.com/fishing.htm

And also find sites like this:
http://usafishing.com/russian.html

If he loves fishing, he may already have preferences, maybe some area
he has heard of but never been.  Also something to try to find out.

Good luck