Depends. My guess is there is hardly a rock or tree where you have dug. Roots, and rocks, can flat humble a person with only a shovel, especially out in mountain country, where it's all river or glacial cobble below one foot. It would take weeks to dig that size hole with a shovel where I have lived in Idaho and Washington. Those boulders 3 to 5 feet around, will leave you scratching your head.
That said, the OP should dig as long as it takes. Except of course, others have done the leg work and shown the truth to the story.