Butternut

After an early-evening outdoor concert at the Hans Herr House in the town of Willow Street, Lancaster County, we were milling around eating ice cream when I spotted these odd fruits on the grass under what looked like a walnut tree.

They were exactly the same yellow-green color as walnut fruits, but with an elongated shape and a sticky, fuzzy surface. We brought two of them home and immediately did an online search.
It turns out that they are from the butternut tree (Juglans cinerea), which is also known as white walnut. The tree is a native of the Northeast, but many of them have been killed by a fungus called the butternut canker. This tree seemed to be thriving.