Oh no! It's not Amanita caesarea. Wikipedia says it is not found in the US: "It is found in North Africa and southern Europe, particularly in the hills of northern Italy. The mushroom is also distributed in Hungary, India, and China . Although the species is not known to exist in the United States and Canada, it has been collected in Mexico." So, still searching....

To me it looks like something in the "boletus" family. They have pores on the underside rather than the usual "gills". Its a large family containing the sought-after porcini mushroom.but also many, many others.

A search for "Dog Vomit Fungus" or "Slime Mold" should get you more info but it is said to be harmless and only grows on organic matter. Anyway, its scientific name is Fuligo septica.

Sorry to disagree gardengal but the term "mushroom" is a colloquial term normally used to denote edible forms of fungus that grow on a stalk, have gills, and a cap of some form. Oxford English Dictionary - "Definition of mushroom - a fungal growth that typically takes the form of a domed cap on a stalk, with gills on the underside of the cap. Many forms of fungus growth do not qualify as "mushrooms" and are potentially deadly. The only forms of Calvatia (puffballs) that are considered safe to consume are those which have a true stalk (the ones Etta posted do not) and are pure white inside when cut open. http://americanmushrooms.com/edibles3.htm Dave