Ceanothus cyaneus is a rare species of flowering shrub known by the common names San Diego Ceanothus and Lakeside Ceanothus. This Ceanothus is found in the mountains of San Diego County, California, and its range probably extends just into Baja California. Most of the remaining natural specimens are in a small area in the hills around Lakeside and Ramona in San Diego County. This is a tall, erect shrub which may approach 5 meters in height. Its spreading branches are gray-green, with the younger twigs a light greenish-brown. The evergreen leaves may be serrated and toothed with hairy knobs, or they may be smooth along the edges. The underside is a lighter green than the upper surface. The flower cluster may exceed 15 centimeters in length, bearing many bunches of flowers along the length of a greenish stalk. The long flowers exhibit protruding yellow anthers. The capsule fruits are about 4 millimeters long.

Ceanothus cyaneus can be tricky to grow in landscaping applications. After the first year, direct summer water will usually kill it, but it will often also die if it can't get it's roots to moisture over the summer. It's best to plant on dry rocky slopes near a damper area, such as a seasonal creek, or near an irrigated area, or even 5-10 feet from a bubbler. It does best if surrounded by rocks or other plants that can shade its roots from the sun. If happy, it produces profuse displays of flower ranging from bright blue to powder blue to dark purple in color. It does best on north facing slopes, but can also handle east or west facing slopes if there is nearby water.