During 4 days of heavy spring rains in 1938 the rivers, streams, washes, etc. began to overflow their banks in the Los Angeles area. This resulted in the 5the largest flood in the area's history. More than 116 people died in the watery rampage as streets became creeks in their own right. It also washed out a then under construction road leaving a bridge stranded in the East Fork of the San Gabriel River (See: The Bridge to Nowhere). The flood left thousands of dollars of damage and an outcry from the public for even more flood control. The result? There are no rivers in the Los Angeles area. They've all been dammed and channelized. There are a few sections of the Los Angeles and San Gabriel Rivers that "look" natural, but that doesn't really amount to much. This also is a problem for rescue workers when people accidentally fall in during a hard rain...since the channels are designed to get water out extremely fast.
But if you want to see real creeks, check out Santa Barbara when I drove past there on the 101 I actually saw real creeks bridged over (There is a difference, namely, no signs of concrete and the very natural look of a seasonal creek, a dry sandy bed). Pretty cool.