Field mustard. Non-native, an invader from Europe. Found along roadsides, on our mesas, and on the lower reaches of most trails.
Easily confused with black mustard (Brassica nigra), the best way to distinguish is to look at the upper leaves, in B. rapa these leaves clasp the stem, while in B. nigra they do not.
Blooms all year but it is at it’s peak Jan-Feb. In most places black mustard predominates except at the bloom peak.
These leaves do clasp the stem.
While those of B. nigra do not.