The alluvial fan deposits underlying Pomona tell a complex story of gravels, sands, and finer silts washed down from the San Gabriel Mountains. Knowing exactly where the coarse-bearing zones transition into saturated clays isn't something you can guess from a single boring log. That's where surface electrical resistivity and Vertical Electrical Sounding (VES) surveys come in: they map these lateral and vertical changes without turning half your site into a drilling grid. In our experience across the Inland Empire, combining a few well-placed borings with a dense resistivity grid gives the most reliable picture of what's underground. For sites near the 60 or 71 freeways where fill material is common, we often pair resistivity profiling with test pits to ground-truth the geophysical interpretations before finalizing foundation recommendations.
In Pomona's alluvial setting, resistivity contrasts between dry gravels and saturated silts are often sharper than what a standard boring log alone can reveal laterally.
