Yep, I do a lot of local riding.
Haven't done Mosquito Ridge, but have done Iowa Hill from the Foresthill side over to Colfax. That last 15% grade on one lane paved with 500' drop and hairpin turns is kinda impressive. Not to mention clench-instilling :wink:
Over on this side, if you haven't done so, a favorite of mine is 49 south from El Dorado to Plymouth, then east on Fiddletown Road to Shake Ridge, continuing east on Shake Ridge to 88. Then 88 east to the top Mormon Emigrant Trail, back west on the MET into Pollock Pines and then back 50 or Pleasant Valley...
Or, from your location in GV, west on 20 to Loma Rica Road, northeast on Loma Rica to Los Verjeles Road straight through Bangor to Oro Bangor Highway to Miner's Ranch Road...north on Miner's Ranch to 162 Oro Quincy Highway, then northeast on Oro Quincy and continuing same after it changes to Bucks Lake Road. Continuing northeast on Bucks Lake/Oro Quincy into the town of Quincy, then 70 east to 89 south at Graeagle, to Gold Lakes Highway south over to 49. At that point, for you, I'd just take 49 south into GV, but you could also continue southeast 89 to Truckee, then pick up 80 west to 20 west and back to GV. Great ride, about 250-300 miles...
Many other places I haven't explored yet. I'm thinking about heading up to Lassen next summer and maybe Oregon and Washington again...