I've been metal detecting for about 3 years, with the last two the most intense, but this isn't that long as experience goes compared to the good folks on this forum, so take this for whatever its worth.
I seem to hunt junky areas a fair amount and also use the Garrett AT Max and a Garrett AT Propointer. In my current location, I do much of my hunting in Zero Mode with Iron Discrimination @ 38. I generally run without Iron Audio and everything notched out below 40 in Zero Mode. Owing to corrosion, I'm not going to find very much in the way of interesting iron here in Charleston, unless its a cannonball. Besides rust, I find coins, tokens, jewelry, brass garden doodads, aluminum gutter snippings and bottle caps and firearm cartridges. I'm hoping to find more silver coins as I widen my search area. I'm keying on the high end ID numbers and tones and digging a lot of 6" plus pinpointer indicated depths, some to 1'. I celebrate when I get a worthwhile target with a 2" depth signal. I do occasionally get some interesting signals that are at the effective depth limit of the AT Max in All Metal mode. I've got to excavate a patch of ground hitting 90s very weakly, but regularly with little Iron Audio growl (at that depth I have to reach for the deepest signal resolution I can get). The dark soil is about 1' thick with blondish semiconsolidated, friable sand below. Most rusty stuff seems to be scattered throughout the dark soil interval. The ground balance numbers are high 80s to low 90s, so the soil is pretty mineralized. There are actually frequent gravel sized black rocks in the dark soil that generate a metal tone on the AT Max (magnetite?). This is probably way more than you want to know.
I get out to Colorado reasonably frequently and lived in the Rockies for many years before retiring to warmer climates. Your iron objects last a lot longer out there than they do here, so close to the sea and with regular brackish flooding. The Rocky Mountains present lots of MD opportunities if you are able to hit the boonies. Charleston is delightful, also, and rich in history. I does get hot and humid and summer digging is best in the shade with a icy pitcher of lemonade nearby. I hope this helps.