These acorns look to fresh to have been buried in the ground. Gray squirrels also cache acorns and other nuts in tree cavities. They eat nuts in the winter and eat buds, seeds, flowers and mushrooms the rest of the year. They also take mushrooms and put them among twigs or in crotches of a tree to dry. The mushrooms are either eaten dry or added to their cache. Squirrels will also gnaw on bones for the calcium.
Gray squirrels build their nests from leaves and sticks, and they also nest in tree cavities. They have 2 broods a year.
Lightning downed this tree many years ago. Mosses, lichens and shelf mushrooms now cover most of the bark. A 4-foot strip of bark is missing on the top of the log, with acorns scattered along most of it. An inch-and-a-half hole disappearing into a more rotten part of the wood probably belongs to a mouse.
This downed tree is in the ravine on my property, and Buffy and I pass it often on our hikes. It will be interesting to watch activities around the log and its decaying process too.