Wow, Idahoan, you are more than a mile or 2 from my gardens. But, I've got some gravel I can sell you.

I think you are on the right track but what do I know? I once "killed" plants in Moscow, there in the the Palouse Hills. Just couldn't make the adjustment from glacial till to wind-blown loess. And now, after 4 decades here . . .

I posted the link below on the soil thread. Maybe it will be of help to you. Some of the ingredients you mention are included in those mixes.

Steve

Here is a link that might be useful: Attra - Potting Mixes

When you make your mound, incorporate your mix into the native to get drainage. Two different layers won't drain until saturated (perched water table) and this will kill roots. I had an area in the yard in Sacramento that I dedicated to hummers & that's where I ended up all the time. You won't regret the extra work and care.

Dan

For the granite, I use chicken grit. You can find it at feed stores in fairly large (and heavy) bags.