It is one of the hot springs. If you look in the center where it drops off, it goes down so far it is scary almost. I just loved the colors and beauty of it and had to capture that dropoff in between the smoke that rises from it.
Stunning park and I recommend everyone put it on their bucket list as a must see. I had no idea how amazed I would be around every corner. I'll likely be adding a few more Yellowstone photos from that trip to this thread.