Fontana's rapid transformation from rural citrus groves to a major logistics hub placed heavy infrastructure demands on a complex alluvial fan. The city sits at the foot of the Jurupa Mountains, where the Lytle Creek and Cajon Creek washes have deposited interbedded sands, silts, and cobbles over millennia. These deposits can change radically within a few hundred feet. A single deep boring cannot capture that lateral variability. An exploratory test pit in Fontana exposes a continuous vertical face, letting the field geologist map stratification directly. In areas north of Foothill Boulevard, older debris flow lobes often hide beneath a thin veneer of topsoil. Identifying these features before construction prevents costly surprises during excavation. For deeper verification, we often pair the pit excavation with SPT drilling to correlate visual observations with N-values in the same geologic unit.
In Fontana's alluvial fans, the soil profile can shift from clean sand to cemented conglomerate in less than three vertical feet. A test pit reveals that transition plainly.
