The water itself is hard. Due to groundwater pumping, subsidence is a problem in some areas, particularly near Woodland. Creek fisheries have been affected in drought years because of water being diverted from the creeks. In the upper bioregion, underlying serpentine belts produce serpentine plant communities, including some rare plants. In the Central Valley, virtually all land is urban or agricultural, and little remains of the original plant communities.
Some riparian corridors survive, with oak, willow, walnut, and cottonwood trees.
Tule and cattails are common in the sloughs. Native plants that once made up the valley prairie, such as California poppy, lupine, and owl clover, appear by roadsides. The lower bioregion is part of the Pacific Flyway. Thus there are abundant hawks and waterfowl during the fall and spring migrations. Many hawks and waterfowl winter here, and some live here year round.