Lemmon's rockcress is tufted perennial wildflower with several simple (or occasionally branched) stems which are spreading to mostly erect, rising 5-20 cm high. Many short, sterile leafy shoots may also be seen. Plants are largely glabrous but may also be densely covered with much-branched hairs. The basal leaves are found in a basal rosette. They are oblanceolate to oblanceolate-obovate in shape tapering to short petioles. The leaves are 1.5-2.5 cm long and 3-5 mm wide and have entire to occasionally few-toothed margins. The blades are covered with dense, gray, felt-like hairs which are much-branched in a treelike pattern. The stem leaves are oblong to lanceolate, sessile with heart-shaped bases, and 0.5-2 cm long. The herbage of the leaves varies from glabrous to covered with minute, felt-like hairs.
The inflorescence is a 3-10 flowered raceme. The pedicels measure 2-6 mm long and the glabrous to softly haired, purple sepals are 2.5-3.5 mm long. The rose-purple petals measure 4.5-7 mm long. The pedicels are short and glabrous. The fruits are glabrous siliques which are ascending to spreading. The siliques are often turned to one side and measure 3.5-6 cm long and 1.5-3.5 mm wide. The pods vary from straight to slightly arched.
Lemmon's rockcress is found on cliffs, talus slopes and in alpine meadows in the mountains.
Lemmon's rockcress may be found from British Columbia south through the Cascade and Olympic Mts. to California and east in the mountains to Montana and Colorado.