We moved into this house about 6 months ago, and as I look deeper into things I find that there were several items left never even started, and a few started but never finished. The one I am currently getting ready to start is the garage (when I went and applied for the building permit they found that there was one applied for back in 2007 before the market crashed

). At any rate, I found that the contractor, or previous owner, or
someone had started on adding the electrical for a garage, but it, along with the garage itself, never happened before he gave up and sold the place!
There is a 2nd main breaker box added to the larger meter/main enclosure, it has wire going to a 60a breaker, but nothing leaving. Obviously I will be feeding the new garage/new panel with this. Leaving this main it will go in to my crawl space, then after about 25' it will go out the foundation in to (24" deep) conduit and out through the yard to the garage.
What gauge wire do I need to run for a 60a panel? 6ga copper/4ga alum?
I have a piece of 4ga service entrance cable that is more than long enough, can it be used in the conduit?
Thanks in advance!