In discussions about shadows, these sorts of odd striations and blemishes are generally referred to as “self-shadow surface acne”. They’re commonly caused by math imprecision when a surface (such as here, the mountain) throws a shadow onto itself. The shadow-caster and the shadow-receiver are so close together (ie: directly on top of one another), that sometimes the math flips their order around. This results in these interesting stripe patterns.
Hope it doesn’t take me too long to sort them out. I’d really like to finish shadows today and get back to items.