It is a large shrub or small tree growing to 4-12 m tall, with gray bark often coated with lichens. The leaves are dark green, palmately compound with five (rarely seven) leaflets, each leaflet 6-17 cm long, with a finely toothed margin and (particularly in spring) downy surfaces. The flowers are sweet-scented, white to pale pink, produced in erect panicles 15-20 cm long and 5-8 cm broad. The fruit is a fig-shaped capsule 5-8 cm long, containing a large (2-5 cm), round, orange seed; the seeds are poisonous. The California Buckeye is a plant adapted to a dry climate; it starts dropping its leaves as soon as summer arrives to help it conserve water.
It can be found along the central coast and the lower elevations of the Sierra Nevada, up to 1700 m altitude. It grows in oak woodlands and is dominant in some chaparral habitats. The tree acts as a soil binder, which prevents erosion in hilly regions. It is sometimes used as an ornamental.
Local native tribes, including the Pomo, Yokut, and Luiseño, used the poisonous nuts to stupefy schools of fish in small streams to make them easier to catch. The bark, leaves, and fruits contain the neurotoxic glycoside aesculin, which causes hemolysis of red blood cells. Indian groups occasionally used the nuts as a food supply, after boiling and leaching the toxin out of the nut meats for several days, although it was not a preferred food. Even the nectar of the flowers is toxic, and it can kill honeybees and other insects which haven't coevolved with the tree. When the shoots are small and leaves are new they are low in toxins and are grazed by livestock and wildlife.