Second year Cimarron which was the top Schwinn ATB model for a couple of years.  The top and down tubes are ovalized at the head tube and fillet brazed.  The seat lug and bottom bracket lug are lugged.  This bike was used pretty hard and is in fair condition but it is pretty tough to find the early Cimarron bikes.  For some reason, Schwinn used high rise bars on the high end bikes and flat bars on the lower end.