The location and character of the Creston fireclay deposit is poorly known; it is described as along railway, best by Goat Canyon. It is most likely a bed of clay in Quaternary or Recent glaciofluvial deposits.
The deposit is described as silty, grey-yellow, slightly calcareous clay; workability is described as 28 per cent water, gives fair plasticity. It is of average shrinkage, 3.1 per cent; tensile strength, 1.72 bars, fit for common brick by the soft mud process. Other characteristics, including cone, absorption and shrinkage, are described in Bulletin 30.