[3] It is mildly poisonous, causing gastrointestinal upset in many individuals.

[4][3] The caps are 5–12 cm (2.0–4.7 in) wide, white, sometimes with a grayish-tan center, dry, and either unchanged or yellowing slightly when bruised.

Since A. californicus is toxic, differentiating it from other similar mushrooms is important.

Unlike A. xanthodermus[5] (a close relative in the section Xanthodermati), A. californicus's yellowing reaction is not always readily apparent and the annulus is smaller.

Even in specimens where the reaction is not immediately apparent the addition of a basic solution such as NaOH or even Lysol will cause the reaction to become quite noticeable, making this a convenient way to distinguish between A. californicus and similar mushrooms.