These large stones are called "glacial erratics".
They are carried by glaciers, sometimes from great distances. When the glaciers melt, they leave the stones behind. Sometimes these huge stones are balanced on small stones or on the edge of scarps or piled on other stones. Stone number 5708 is the size of a school bus.
These particular erratics are exposed in the open on the coast. The vegetation is inhibited due to salt spray from the ocean. Most erratics are found in the forests that have grown since they were deposited about 12,000 years ago.