The cyclist was hit by a light-colored SUV on Mt. Diablo Boulevard near Bont Lane around 4:20 p.m.
After hitting the bicyclist, the car was last seen making a left turn onto southbound Bont Lane, police said.
Police said the bicyclist suffered a head injury but is expected to make a full recovery.
The driver is described as a white female with dark hair pulled back into a ponytail.
Anyone with information about the collision is urged to call Officer Mike Adams at the Walnut Creek Police Department at (925) 943-5844.