Tough to guess on pH and only a soil test would tell for sure. Dax is growing a myriad of conifers in soil with a pH of 7.0 so it's likely more a matter of do you want several small ones, a few mediums, one or two larger or a mix of all of the above. And then there is color...and shapes...and...

A picture of the area might help as well.

tj

I could only recommend you use seedlings of Picea omorika - Picea orientalis - Pinus aristata - Picea engelmannii - Pinus flexilis.

If you want to grow dwarf and miniature conifers - they will need to be grafted to the above seedlings for rootstocks. This will require that you have plants, custom-grafted. Gee Farms I know will custom graft. You'd also be best-suited to stick with these conifer species of dwarf and miniature, too. So you will want, Pinus flexilis cultivars grafted onto Pinus flexilis or Pinus aristata (or vice-versa) and all the Picea's (spruce) grafted to one of the species, mentioned. Also, add Pinus heldreichii (leucodermis) to your selection(s). Pinus heldreichii/leucodermis is a 2-needled pine and is different from aristata or flexilis so all Pinus heldreichii will need to be grafted to the root systems/rootstocks of Pinus heldreichii, only.

Maybe I'll think of some more options. While my own soil is 7.0, it has no gravel (your ph might be much more). Get yourself a 5 or 10 dollar ph tester and see what the meter reads. I think you should do that first. The good thing about your gravel is that is provides the ideal conditions that the Rocky Mountain conifers, want:
Pinus flexilis
Pinus aristata
Picea engelmannii

I'll read about Abies lasiocarpa as that well could be another addition to your plantings.

Dax

Picea pungens - I forgot. You should have all your Picea's/Spruces grafted to this. A very common grafting rootstock.

Abies lasiocarpa likes gravely sites but the ph they prefer is 6.8 or less. The last thing you could do is use either Alfalfa meal or pelleted Sulphur each spring, while monitering ph to keep it at where you need it. A ph of 7.0 or lower will accomodate most conifers.

Good luck!

Dax