Putah Creek, below Lake Berryessa, has great winter time C&R ff only fishing. it's put and take from april to nov and ff only during the winter. tailwater (bottom draw, so it stays the same temp all year) and lowland, so you don't have to contend with snow drifts on the banks.
the water will be low in the winter (good for this creek) and the fish will have at least one season under their belt, so they won't be pushovers. lots of two or more year holdovers, though, to make it interesting, and a good proportion of stream born fish as well. fish in the 12-14 inch category are normal (those planters), but lots in the parr size and many in the 16-22 inch size too. some bigger fish can be found (a 17 lb brown was caught when I was in college there about ten years ago).
re: the browns, they haven't planted browns there in years, but there's a self sustaining population of them. the slower sections will have the real beasts, and rainbow parr patterns should be able to entice them to come out to play (although I got my best brown, a 24" hook jawed male on a #20 black AP nymph).
The uppermost section is pure tailwater, down to the campground. below that, there's a section that fishes like a freestone creek. from there, long slow sections (almost like limestone creeks) are interspersed with riffly sections. as expected, bows and smaller browns in the fast sections, browns and some bows in the slower ones.
if you do fish it, think small. most bugs up there are in the #16-#20 range and dark, and the fish get a lot of pressure throughout the year anyway. darker AP nymphs, dark olive hare's ears, dark GRHE's, and PT's (all with bead heads or not-your choice) are my favorite patterns, but anything small and dark fished deep will work. there's some rising action to baetis some warm afternoons, but not enough to hang your hat on. also, some sporadic caddis action can be found, but don't count on it. For tippets, 6X is my standard. the water is stained, so I'm sure you can get away with a little heavier, but I need that small a tippet to get through my small hook eyes anyway.
also, at that time of year, the fish may be on redds (check up around the dam and the campground for redds). if so, glo bugs should work in the faster sections below. please don't fish to the spawners: there are enough idiots who do it already.
drop me a line if you want to check it out. I can give you more details if you need them.