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Pisolithus arhizus
stemmed 2 inches tall, 1 3/4 inches diameter, pebbly surface
spotted in grass on riverfront property
I've added a final photo showing that the surface has turned to a dusty mass of spores. ID updated as well.
Thank you both for the suggestions. I have looked at both links, but I'm still unsure (though Pisolithus arhizus seems the more likely candidate). I'm still observing the fungus to see how it progresses.