Clarkia are a lovely and varied group of flowers–there are seven different species that are listed for Marin alone. These four-petalled beauties are almost always pink, and often look very similar to one another. They are often generically simply dubbed Clarkia, or Farewell to Spring.
If you look close, reddened Clarkia (Clarkia rubicunda) are distinguished from their cousins by having ordinary petals that aren’t dramatically narrowed. The flowers are either solid pink or have a red splotch at their base (but not elsewhere). Their unopened buds are erect, not drooping, and the young, long seed pods are notched with four distinct ribs. Luckily, each stalk bears several flowers that open consecutively, so in a patch it is often realistically feasible to find both these diagnostic traits at the same time.