It's called the Golden State for a reason

Most people think it's because of the sunsets or the Gold Rush. But California is actually nicknamed the Golden State because -- much like Eastern Oregon and Washington -- throughout the state's interior, most native, drought-resistant grasses have been replaced with drought-sensitive European grasses which die off during the hot, dry summers. The growing season is actually inverted in the Central Valley from most of the rest of the world: summer is the harsh, inhospitable time of year during which plant life mostly goes dormant; it's our mild, wet winters that are the primary growing season.

In average years, there simply isn't enough water to keep ordinary grasses and other small plants green throughout the summer. In drought years -- which are not uncommon -- it's even more impossible. Thus, the maintainance of the ridiculous acreage of lush, green, non-native grass lawns consumes over half of residential water use in the most arid areas, which have seen the most development in the past few decades.