Preparing bed above shallow bedrock. Advantages?

I live in the Rocky Mountains. Very rocky. My zone 0 is 6-10 inches of soil above hard decomposed granite. It’s rock that will break apart with heavy equipment.  The area I’m talking about it only 10’x20’.

Last year I planted tons of Dikon radish to help break it up. Sadly the soil was too shallow to hold water in the hot Colorado summer and they died with little progress in the roots.

My neighbor had an bobcat with a trencher that amazed me with its ability to crew through this decomposed granite!  Previously I rented a bobcat but didn’t think of the trencher attachment.

I decided to raise the soil in this area another foot or two.  I planned to plant annual greens with shallow to medium root systems.

But should I have rented to bobcat with trencher to break up the decomposed granite underneath it all first?

Is there any advantage to having this hard layer underneath?  Perhaps holding in moisture instead of it sinking down?  

In early spring when the snow melts this area is water logged, and along with the later spring rains. But summer on there isn’t a problem and I’ll need to keep it watered.

I plan to compost on the area in the fall and by October it will be covered in snow until April.  

Hi Seth,

Seems like we are in similar contexts. I am in the Siskiyous of NW CA. While we get weather a bit wetter and milder, our zone 0-1 is also bedrock, but in our case its largely serpentine. I have done hugels with moderate success on pavement before, so I figured it could work here to bury woody debris in this bed for moisture retention. We used primarily fir bark because that is plentiful and seems to be the best part of the tree for hugels in my research and experience. We layered coffee grounds on the bottom just above the first wood layer, and on top of the bed as mulch. We also added some Wilson fur (our Pyrenees-Anatolian in picture) in the bottom layers for nitrogen and possibly rodent deterrence (or maybe it'll attract them as nest material!). We also mixed in liberal amounts of oyster shell for calcium that is deficient in our soils (not that we have any right there). We filled in the rest with reused potting soil that has been stretched with sharp river sand. It will need to be irrigated in summer, but I am hoping the adjacent rock jack and rock frame to the bed will help condense a good amount of moisture, and we will keep it mulched or densely planted with herbs and shallow rooted veggies. It also received roof runoff just uphill, so when it is wet it could get too wet, and hence we had to balance drainage and moisture retention, which the wood is great for. Best of luck!

Interesting hugal!  This gives me hope.  Thanks!