Spea hammondii, the Western spadefoot toad, is medium-sized with adults reaching up to 65 mm in SVL. The skin is loose with small vertebral tubercles. The head is as wide as the body, having a rounded snout with an upward tilt and large protuberant eyes. The parotoid glands are small and not distinct. Forelimbs and hindlimbs are short and stout, with the foreleg having dorsal tubercles. The feet have well-developed webbing between the toes. The main distinguishing features are the single semicircular black "spade" (keratinized inner metatarsal tubercle) on each heel, and vertical pupils.
The dorsal ground color ranges from light green to gray with scattered darker splotches. A pair of light-colored spots is generally present, one on each side of the anus. Body tubercles can be orange to somewhat red. Usually a pair of light-colored paravertebral stripes is present, extending from behind the eyes. Ventrally, the color is whitish to creamy-yellow.