Clarkia williamsonii is a species of flowering plant endemic to California, where it is known from the forests and woodlands of the northern and central Sierra Nevada foothills.

Clarkia williamsonii is an erect annual herb with linear to lance-shaped leaves each a few centimeters long.

The inflorescence produces opening flowers and buds which are closed except for the tips, where the sepals do not fuse.

Each fan-shaped petal is up to 3 centimeters long and is usually lavender with a white area and a purple spot in the middle.

A unique feature of this species is its tendency to have widespread reciprocal translocations.