I was reading some state propoganda on morels in Missouri. I say propoganda because I am not too sure about all of this information. According to the Missouri Department of Conservation black morels tend to fruit more prolifically than yellows. Yet I have never been able to find a single black morel in Mid-MO and have been able to find very prolific patches of yellows. Maybe this is more true in southern Missouri where there are rampant reports of black morel finds.

Here's the link to the article in the Missouri Conservationist: The Wild Morels
Here is another state web page on morels: Missouri's Magnificent Munchable Morels

Here is a picture of a yellow I found today. Only found ten but they were big. All of the ones I found had fallen over and were laying on their sides.