Calycadenia truncata is a species of flowering plant in the daisy family known by the common name Oregon western rosinweed. It is native to southwestern Oregon and northern and central California. It is found in the Cascades, the Coast Ranges, and the foothills of the Sierra Nevada as far south as Monterey and Tulare Counties. Calycadenia truncata is an annual herb producing an erect, reddish stem, which may exceed 100 cm (39 in) in height. The leaves are linear (long and very narrow) and up to 10 centimetres (3. 9 inches) long. The inflorescence bears one or more flower heads at separate nodes, surrounded by short bracts tipped with resin glands. The hairy flower heads have a center of many purple-tipped disc florets as well a few yellow ray florets. The fruit is an achene.