[5] The mature tree has a grayish to reddish brown trunk with scaly, furrowed bark.

The leathery leaf blades are often concave and are an oblong lance shape or oval with pointed or rounded tips.

Though it is now limited to the islands, it was once widespread in mainland California, as evidenced by the many late Tertiary fossils of the species found there.

[5] Recently, it was found that there was a high genetic variability across many of the Q. tomentella populations, but this variation was not evenly distributed.

[5] The island oak was listed as an endangered species by the International Union for Conservation of Nature.