Map showing the approximate geographic position of the back-reef evaporite
(E) to carbonate (C)
transition in various Guadalupian shelf units in the Guadalupe Mountains. The progressive
eastward shift of the transition zone through time reflects basin filling and eastward progradation
of the shelf edge through this time period. This geographic shift, coupled with the eastward structural
tilt of the Guadalupe Mountains, also explains why one has to travel so far west on field trips to find
evaporite facies. More easterly, evaporitic strata in younger units have simply been eroded away.
Adapted from Bjorklund and Motts (1959) and Motts (1968).