Hi Alan, thanks for using Ask Extension.

Based on your pictures and description, the circular patches could be the result of a few different things like fungal "fairy rings", old soil disturbance, patchy weeds, but a closer look would help narrow it down. 

If you could you send a few close‑up photos of the circles? (You may have to send them in more than one post.) Here’s what would help the most:

-  A photo taken standing directly over the edge of a circle to show the transition between the normal vegetation and the ring.

-  A close shot of the plants inside the circle like individual leaves, stems, or weeds if present.

-  A close shot of the plants forming the ring itself especially if the color or species looks different.

-  If possible, a side‑view showing height differences between the ring and surrounding area.

Also, note the type of soil (sand, clay, loam), and any noticeable differences at these locations (e.g. soil moisture, soil color, debris)

Hopefully with additional information we can figure this out.

I look forward to your response.