Slightly crusted back mole what could it be?

Seborrheic Keratosis. A seborrheic keratosis usually appears as a brown, black or pale growth on the face, chest, shoulders or back. The growth has a waxy, scaly, slightly elevated appearance. Occasionally, it appears singly, but multiple growths are more common. Seborrheic keratoses don't become cancerous.
Black moles worry me. My first concern would be that you could have a melanoma, which is a serious - but treatable - form of skin cancer. I am concerned about any dark black mole, any mole that itches or bleeds spontaneously, and any mole that has multiple colors in it, or any large mole. Because you are from colorado, you have probably had a bit of sun exposure, which places you at higher risk. Please get this checked.