Here's what they look like after the tops were cut off & I washed these mutated knobby..."things". Aren't they ugly? I did a google search to look for possible answers. Here's what I found out: If you have heavy clay soils or rocky ground with low fertility or if you planted your carrots too close together - less than 2 inches apart -- you may see this problem. Hot weather may also trigger root problems and, when followed by periods of wet weather, will cause roots to expand rapidly and develop cracks.
We certainly didn't have hot weather here in northern IL this summer. I think hubby planted the carrots too close together. Yep, I'm blaming him. :-) Oh well, now we know for next year!