Well a 4' tall bank is almost impassible to a 2x4 from water, for a 4x4 is doable but it would be hard maybe impassible too. What you do is get a comalong, attach it to a tree and a rope to your quad and pull it up. Or drive down the river and see what other options you have. I have driven in alot of rivers and there is always an easier spot, you just may have to cross some deep water.