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The Formación Roja is the lower unit and includes clays, siltstones, argillites, and shales. These are strongly cemented by mainly gypsum and also calcium carbonate, which occur both in the rock material and as infill of the discontinuities. The gypsum cementation gives the Red Formation claystones a high strength and gives the rock a massive appearance. The upper "Lake roof formation" consists of interstratified layers of limestone and marl, but can be divided into two units: one of dominantly limestone and another of dominantly marls. The units are generally jointed and occasionally faulted. The thickness of the layers is generally on the order of decimetres. Thicker layers occur; most are less than 1.5 - 2 meters thick. In this formation a few erodable clayey layers occur.
The upper "Lake roof formation" consists of interstratified layers of limestone and marl, but can be divided into two units: one of dominantly limestone and another of dominantly marls. The units are generally jointed and occasionally faulted. The thickness of the layers is generally on the order of decimetres. Thicker layers occur; most are less than 1.5 - 2 meters thick. In this formation a few erodable clayey layers occur.
I'm not (yet) a star in engineering geology, but in structural geology, the bit about gypsum should've set off alarms. Gypsum is the earth's ideal lubricator. A third of Greece slides on a 10 centimeter band of gypsum, exposed at the surface. It doesn't take much pressure to change gypsum's viscosity, and slide you go.
If you'd know some more links/literature on the geological aspect, I can have a look...
