the zagros ftb extends for about from the bitlis suture zone in the northwest to the boundary with the makran trench, east of the strait of hormuz, in the southeast. the belt varies in width with two main salients (where the thrust belt bulges out towards the foreland) in the lorestan and fars domains and two main embayments (between the bulges) at kirkuk and dezful. the variation in geometry along the strike is attributed to the distribution of the late proterozoic to early cambrian hormuz salt layer, with a thick and continuous salt being present beneath the salients and either missing, thin or discontinuous in the embayments. the distribution of the hormuz salt is controlled by the extent of late proterozoic basins. the belt is also divided into zones from northeast to southwest. next to the main zagros reverse fault is a zone sometimes referred to as the 'high zagros', the highest part of the zagros mountains reaching heights in excess of , with the 'high zagros fault' forming its southwestern boundary. the next zone between the high zagros fault and the main frontal fault (also mountain front flexure) is known as the 'simply folded zone', characterised by many elongate folds and very few surface faults. the zone to the southwest of the main frontal fault is considered to be part of the foreland basin although active structures are observed as far out as the zagros frontal fault.