Subsequent periods of glacial activity alternating with warming trends caused further shifts in the types of vegetation. As conditions changed, species evolved to fill newly-created habitats. Older species continued in restricted pockets of previous habitats, known as refugia. The coast redwood is also a relictual species, although its refugium still covers a relatively large area of the coastal part of the state. The distribution of plants in California today has thus been heavily influenced by the past climates and geologic history.
Many species are rare because they require habitat conditions that are no longer prevalent.
These plants have specific needs met by a unique combination of habitat factors not often duplicated. One of these unique habitats is a vernal pool. Vernal refers to spring. These small pools, or shallow lakes, fill during winter rains and dry during the spring to become covered with flowers. This restricts water percolation into the soil so it remains until it is evaporated in the spring.