If you follow Pasadena Rd. down towards Bullock (going towards 72) you'll notice a dirt road leading into the woods, right where the RR tracks cross Pasadena Rd.
If you go down that road, there are some trails that will lead you to the clay pits - marked as "Old Half Way" on Topo Maps.
Look at
www.TopoZone.com for topo maps of the area.