Go to Lone Star BMW and get a copy of MapVenture's South Central Texas map, $5.95. It doesn't distinguish between dirt and pavement, but it does cover almost all the county rds. in the area. Get a handlebar mounted map pocket and you'll be good to go.
I am more familiar with Bastrop, Caldwell, Guadelupe, and Gonzales counties.
There are some good dirt rds north and east of Bastrop. CR's 179 and 49 lead north to Elgin. North of the State Parks, CR's 146, 153, 159, & 196 were all still dirt the last time I was out there. Part of the CR that runs just north of SH290 between Elgin and Paige was dirt.
I remember there being some dirt rds east of Thorndale, near the old AMSA CycleParks lease (CR434?).
The powers that be keep "improving" the CR's, so you may have to put in some miles on pavement to get to the real rural areas. Such is "progress"...
PM me if you want to haul down here and go exploring, weather permitting.
PS- You show definitely arrange for time off to do the Texas Adventure Ride in Junction next April. You will have so much fun!
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Alphadog
Rollin' on, from two wheels to three...