Abstract
This study involved constructing a structural, hydrogeologic framework, and textural model of water-bearing units in the Rialto-Colton Basin and parts of the Chino, and North Riverside Basins (referred to as the Chino and North Riverside areas). The models were based on available borehole lithologic and geophysical logs, and water-level data. Data and interpretations from previous structural and geophysical studies were evaluated to update fault locations in the Rialto-Colton Basin. Fault locations were updated based on previous InSAR, gravity, aeromagnetic, and seismic studies. The hydrogeologic framework model is based on the water-bearing units defined by previous studies (Woolfenden and Kadhim, 1997). Borehole lithologic and geophysical logs were used to determine boundaries between these water-bearing units, which were then interpolated throughout the study area. The boundaries of a perching layer in the Rialto-Colton basin were determined using a similar approach. The resulting framework model indicates that the stratigraphic boundaries of the water-bearing units generally follow the elevation contours of the land surface. The perching layer was determined to extend throughout most of the middle and northwestern part of the Rialto-Colton Basin, and its thickness varies from more than 50 feet in some parts of the basin to areas of minimal thickness around the edges where it pinches out. The Upper and Lower water-bearing units in the Rialto-Colton Basin generally thicken to the northwest and thicken somewhat to the northeast. The two uppermost water-bearing units in the Chino and North Riverside area, Chino Layer 1 and Chino Layer 2, thicken somewhat to the northeast. Chino Layer 3 thickens to the southwest. The texture model of the study area simulated the distribution of the percentage of coarse sediment. Borehole lithologic and 16 inch normal resistivity logs were used to estimate the percentage of coarse-grained sediment from each borehole. The percentage of coarse-grained sediment was determined along 10 foot intervals of each borehole. The resulting percent coarse values with depth at each borehole were then interpolated to obtain a three dimensional textural model of the study area using water-bearing unit boundaries and fault boundaries as interpolation boundaries. Coarse sediment distribution in the Rialto-Colton Basin was variable over much of the basin. There was a general trend of finer sediments with depth. The southeast part of the Rialto-Colton Basin contained the highest percentage of fine sediments, with areas in the middle part of the basin containing high percentages of coarse sediments. In Chino and North Riverside area coarse sediments were determined to occur along the northeast boundary between Chino Basin and Rialto-Colton Basin. Fine sediments were determined to occur throughout most of the North Riverside area.