How to determine depth of foundation on existing detached garage
You only need check one location. As I remember a 32" frost line, so a 3 ft hole with a shovel does not sound like much of a job. I hand dug a pond 3' deep X 11' long X 6' wide , not that big a deal. Worth getting a fiberglas handle shovel if you don't have one. For a small hole like that a "clam shell" post hole digger may be helpful.