A single flower opened on this little cactus last week. Today, it has five beautiful pink flowers. Click on the image to enlarge.
I found this reference to the little cacti that dot the hill behind our house at BirdandHike.com:
Common Fishhook Cactus (Mammillaria tetrancistra) is a small, mound-shaped cactus with short, thin white spines that nearly cover the plant plus longer, darker, fish-hook shaped spines that stand out from the body of the plant. In early summer, red to lavender flowers emerge from the side of the stem that are nearly as large as the entire plant.