An arch which opens upwards in a ‘u’ shape is called a syncline. Here Wadi Al Mayh flows directly across a huge syncline formed in limestone. The Permian limestone was deposited as horizontal sedimentary layers on the sea floor around 250 million years ago. The limestone layers were later buckled into a syncline following huge pressure from the North East as a result of the Oman ophiolite mountain building, and uplifting of the Arabian plate.