These are Indian grinding holes. These holes are made over generations of Indians using pounding rocks to grind acorns. Some of these holes can be 2,000-3,000 years old. The Indians had to smash up the acorns and cure them because think about it nobody can just eat a raw acorn it’s to crunchy and you can get sick from eating them. 
These Indian made holes are very rare to find and are usually found in large dry forests where Indians used to live. The holes are usually carved into very large boulders because if they were carved into small rocks the rocks would eventually split in two.