I don't think Crappie make as deep a depression as a Bluegill, and they don't always make their beds on loose bottom contents (sand, muck, mud, pea gravel) so it can be hard to distinguish where the bed is located with your sonar. I've even seen a TV angler catching them "bedding" on the fins of outboard motors of boats moored at a marina
Not all lakes have "vegetation", so Crappie (Black Crappie especially) will "make do" with what's available. I've gone down a bank that transitioned from rock ledges to shallow sand/pea gravel .... catching Black Crappie off the rocks, then White Crappie off the pea gravel (so long as there was a small piece of waterlogged "wood" lying on the gravel bottom).