I can answer that question quite seriously...if you want to find "stuff", not just a pile of rocks or the empty hull of a dwelling...you have to go exploring.
Virtually everything I've found has been off the beaten path...like getting up in the morning and going in the opposite direction that everyone else is going. I don't think there are any large structures that remain unfound...but there certainly are granaries and campsites that hadn't seen a visitor in a thousand years before I got there. I've met some guys that are also hardy hikers/backpackers who also have found undisturbed sites...and when they told me where they were I thought, "Well now, you're an explorer, aren't you?".
Nooks and crannies....it's all about those nooks and crannies that you would think no one would bother climbing up to...but those Indians were everywhere. You gotta be a strong hiker and prepared to go all day without finding a damn thing, but you don't stop. It could take several weeks of hiking just to find a few sites.