This common weed is found all over the world and in some countries is considered a damaging invasive species. Growing mostly in disturbed ground it can cover entire fields if they are left fallow. The tiny flowers (15-20mm) can be violet, white, yellow and variations of all of those. They grow on a stalk from 1' to 3' tall and are an important source of pollen and nectar for honey bees in the early spring. We also find the plant in suburban and urban environments where disturbed, untended ground is found along roads and fences. It easily invades flower and vegetable gardens.
These are the darkest flowers I have seen - this picture was taken outside of San Juan Bautista and was part of the overall image above.
This Wild Artichoke (cynara cardunculus) gone to flower is so much the same color as the radish flowers above that I had to include it here. Much smaller than the cultivated kinds, these are also good to eat, but only before they start to flower. The tiny heart or choke doesn't make much of a taste, but if you can collect enough of them you can use them in recipes written for store bought artichokes. They taste about the same, but I think it is too much work and too prickly to get enough to actually use in cooking.