I find these early grey ones within about 10-20 yards of the river. It's kind of a flat that gets flooded when the river gets up and it gets full sun morning, day, and evening. There are lots of ash, elm, and big maple trees. I found most of these growing in the maple leaf litter, but that's not a definite because I find just about as many that are just out on open ground. I'm sure the trees have something to do with it, but not certain what role they play?
I've looked in other areas that are nearly identical and didn't find a single mushroom. Soil type, soil temp, and moisture probably plays a bigger part in where they grow and why than any other variable. Of course the spores have to be present for them to grow and maybe some areas just don't have 1 or several of those variables? Just get out and comb the bottoms and keep going back every few days because they literally grow full size overnight. One day there is nothing and the next day there are shrooms all over the place. Also you might ask around to see if there's an experienced shroomer in your area that wouldn't mind tagging along with you and help you find the best suitable areas on your property. Then split the rewards down the middle.
That's the best advice I can give.
Good Luck!