It contains 1 to 60 percent, pebbles or soft shale fragments by volume. Reaction ranges from slightly acid to moderately alkaline. The Cr horizon is soft shale and ranges from strongly acid to moderately alkaline. This is the Boyd series. Boyd soils have less than 60 percent clay in the Bss horizons.
Opal soils are on level to moderately steep uplands.
Surfaces are plane or convex, and slope gradients range from 0 to 25 percent. Gilgai microrelief is on most landscapes. Opal soils formed in residuum or locally transported clay sediments weathered from soft shales. Mean annual air temperatures is 44 to 49 degrees F. and mean annual precipitation ranges from about 16 to 20 inches. These are the Bullcreek , Chantier , Dupree , Hurley , Labu , Lakoma , Promise and Sansarc soils.