Based on your first post I'll assume you have spoken with the county building department and need the engineer per county requirements. If not, this would be a different conversation. e-mail my friend Scott Schaefer email@example.com
as he works the front range area and may have names. Otherwise x2 on google "geotechnical engineer park county" .
I doubt you would need caissons for a garage in all but the most unstable, sloped, or wet areas. 99% odds are you will have a "thickened edge 4" slab on grade of 3,000 PSI concrete reinforced with wire mesh, with the edge going down as deep as the local frost depth requires." For greater strength you could go to 6" and rebar. Either way there will be rebar in the edge grade beam. Additional compaction work is only required if you place fill material, and there are many methods. Decomposed granite will probably not require any compaction.
Pole barns are nice options too.
Why I know all this is 15 years of real estate law and having built 3 spec houses.