In general, this species has a blue head, wings, and tail; a gray-brown back; grayish underparts; and white eyebrows.

They feed on small animals, such as frogs and lizards, eggs and young of other birds, insects, and (particularly in winter) grains, nuts, and berries.

[4][3] California scrub jays, like many other corvids, exploit ephemeral surpluses by storing food in scattered caches within their territories.

[6] Western scrub jays are also able to rely on their accurate observational spatial memories to steal food from caches made by conspecifics.

The brain-to-body mass ratio of adult scrub jays rivals that of chimpanzees and cetaceans, and is dwarfed only by that of humans.

Scrub jays are also the only non-primate or non-dolphin shown to plan ahead for the future (known as metacognition), which was previously thought of as a uniquely human trait.

[16] However, jays have been observed employing raptor-mimicking calls without the presence of other birds, making the precise adaptive reason for this behavior unknown, though it may be two-fold.

[18][19] Nests are built low in trees or bushes, 1–10 m (3.3–32.8 ft) above the ground, primarily by the female, while the male guards her efforts.

The nests are sturdy, with an outside diameter of 33–58 cm (13–23 in), constructed on a platform of twigs with moss and dry grasses lined with fine roots and hair.

[2][20][21] Beyond the close relationship of the "California" and island scrub jays, resolution of their evolutionary history has proven very difficult.