I've lost a few California wonder peppers this year to what I believe to be blossom end rot. I see it in tomatoes occasionally and although this doesn't quite look the same, I believe it is. Could be a calcium deficiency. Thinking back to what I put in the container this plant grows in, I wouldn't be surprised. But I think it's more likely a problem with water. I've been subjecting my peppers to an unbalanced watering schedule and that might be interfering with calcium uptake. Maybe next year I'll try growing these in a self-watering container.