S. flavescens is a thin-stemmed annual herb growing large, lobed or toothed leaves up to 22 centimeters long around its base, and smaller, less toothed leaves along its gray-pink to brown stem.

At intervals along the upper stem appear cream, yellowish, or very pale purple flowers, each somewhat cuboid in shape and about a centimeter long.

The tips of the petals around the mouth are curled, flared, or claw-like.

The fruit is a thin silique up to 9 centimeters long.

This species is endemic to California, where it grows in the valleys and mountains surrounding the San Francisco Bay Area.