 The Virgin and Santa Clara rivers flow through the St. George valley and converge near the western base of Webb Hill.In southwestern Utah, soil and rock formations are red in appearance due to the presence of iron oxide, although portions of the older section of the city, particularly the southern part near the Virgin River, lie on floodplain alluvium, but much of St. George proper is built directly upon Jurassic, Triassic, and Permian period sedimentary bedrock.The following formations, listed in chronological order, are within the city limits.