Lake or Not?

My new neighbors for a couple of days are a couple of rock hounds. He is an amiture geologist and retired Air Force Colonel. I was talking to them and told him it looked like the whole area my land is located on had been filled in with the same soil you see piled up everywhere from mining years ago. He told me that is volcanic ash. I always thought volcanic ash was black, but evidently not. They are both great and I'll hate to see them leave. Have injoyed talking to both of them very much and they have given me a quickie education on some of the different types of rocks they have found in the area.

Now.... ever since I saw the land on google earth I thought it had to be an ancient lake and he said it probably was. Anyway from looking at the soil while I was out that way a while back it sure appears that rather than make mounds like everywhere they may have just filled in an ancient lake. There is no creosote growing on it... its all the grass seen growing between the creosote bushes everywhere else. If it was actually a filled in lake I wonder what the reason was for? I wonder if it would make good farm land. The native grass sure seems to like it.