The Carrizo Plains are technically part of the Coast Ranges, separated from the main valley by the low ridge of the Temblor Range, but the dry flat valley floor is very reminiscent of the Great Valley. Protected by intervening mountain ranges that discouraged water development, and by low gas and oil potential, the Carrizo plains have generally escaped that kinds of changes that have irretrievably altered most of the original prairie lands of California. Some dryland farming took place here decades ago, and cattle graze in the region, but on the 250,000 acres of the monument one can find the pronghorn antelope, tule elk and other animals that once ranged across the whole Great Valley.
The monument is of extreme geological interest as well. The valley floor is an enclosed basin: water draining into the valley does not flow out, but instead fills the basin of Soda Lake (in the photo above). Interior drainages like this one are not "normal" and when they show up, faulting is often to be suspected. In the case of the Carrizo, the fault is a major one: the San Andreas, the transform fault that separates the North American plate from the Pacific plate. Wallace Creek, at the north end of the monument, may be the most famous example of an offset stream in existence. Almost every pictorial description of the San Andreas fault will include aerial photos from the monument (a shot of the park was also used as a plot device in the original Superman movie). In the picture below, the fault has formed a small enclosed graben valley.
Lest you get the wrong impression, I visited the monument in March of a very wet year. Most of the time the grass is brown, and it can stiflingly hot in the summertime. The park's educational center is open only from December to May at this time, and facilities are very limited. But, it is a wonderful place to explore!