I find them next to all kinds of trees, but never in my life by a elm or ash, and those are what everyone says to look for. I'll tell you what I look for is squirrel trees. The mature trees that squirrels like to use are my focus, probably have found more next to water oaks than any other single kind of tree, but they are by sycamores and red cedars and black haw bushes and slap in the middle of a pasture too. The roots (and that's not what it is- the hairlike, root like mass is the real body of the mushroom) of a large patch may be decades old and produce every year, if weather cooperates. I did know of a 4'thick soft maple in a yard in town that made 20-40 each year for several decades, the tree was cut 6-8 years ago and my friend is dead now, so I don't know if the morels still come back or not.
And they say the grey morels are baby yellow morels- the things can get bigger every day for up to three weeks and turn lighter with sun exposure. Neat thing to look at- google up "time lapse morels" for 15-27 day videos of pencil size fungus getting to be big. If you find some that are pinkie size, flag them and come back every day to watch them mature.
I have a theory, unproven, that some kinds of trees create raised mounds with their roots, thus making an area that doesn't hold piles of leaves and has sun exposure that encourages the morel to fruit, the raised area being some what bare also makes it easier for guys like me to see the morels. The same thing is true on those side hills; leaves blow away leaving relatively open ground for me to hunt. I have wondered how many hundreds of them that I have walked past and never seen because of deep leaves around them?
Got 2+ inches of rain yesterday and cooled from 87 Fri down 32 this morning so maybe my season isn't over yet.