Weathered granitic rock has been shown to have appreciable porosity and water holding capacity. It plays a significant role in water and plant relationships, especially where soils are thin in arid and semi-arid regions. The objective of this study was to assess the rate of porosity formation in granitic clasts. The study site is a series of moraines near Bishop, CA on the east side of the Sierra Nevada. These moraines have previously been dated using cosmogenic surface dating techniques. The ages of the moraines can be used to approximate the length of time the rocks have been weathering. Clasts were collected from the upper 80 cm of soil on four of the moraines, with estimated ages of 19, 65, 120, and 160 ka. Porosity was calculated from bulk density and particle density measurements.