I know that at a land crossing, a citizen can get in without a passport or an expired one. Once they verify your info of course. LPRs can get in too if they have expired GC or don't have it on them, but they have to be in status and pay a 500+ dollar fine. An expired GC denotes just the expiration of the document, not the status. This was straight from the mouth of a CBP officer at San Ysidro.