There are two types of grassland that occur in the Santa Monica Mountains: native perennial and non-native annual grasslands. Perennial bunch grasses are considered to be the original native grassland of California, while annual grasses were those introduced by the European and Spanish settlers for their livestock. The golden rolling hills of California are largely a result of the introduction of these annual grasses, since bunch grasses often remain green even during summer drought.
Perennial bunch grasses differ from annual grasses in that they put much of their energy during their first several years into establishing a well-developed root system that would sustain them through regular summer drought. Their roots penetrate deeply into the soil, providing nutrients and water and holding soil particles firmly in place. This decreases the erosive effects of wind and water. Unlike annual grasses, they don't produce seeds the first year, but as the years continue, produce an abundance of seed at maturity.
More than 100 years of livestock have been grazing on California's former native perennial grassland, which has been converted to non-native annual grassland. Native perennial grasslands historically covered nearly 20 percent of California, but today cover less than 0.1 percent. Today, approximately 10 million acres, or 17 percent of California, is considered valley grassland that contains both non-native annual and native perennial species.