Breached anticlines can become incised by stream erosion, forming an anticlinal valley. Rollover anticlines are anticlines related to extensional normal faults. The evaporites of the area formed more unusual "salt anticlines" or linear regions of uplift. In the folded system anticlines erode into the highest and longest massifs of the Apennines. Convolute folds are complicated folds in beds into irregular anticlines and/or synclines. In extension, listric faults form rollover anticlines in their hanging walls. The crests of the anticlines on both sides have been eroded away. It is the relative ages of the rock strata that distinguish anticlines from antiforms. The sandstone anticlines were much more resistant to erosion than the slate filled synclines. Jabal Akhdar and Saih Hatat, which are large scale anticlines. There are three major anticlines and synclines in Montour County. All anticlines and synclines have some degree of plunge. They usually flank the sides of anticlines and display opposite characteristics. Anticlines and faulted anticlines are the structural features that are also responsible for trapping oil. According to Exploration Directorate of NIOC, there are about 150 unexplored anticlines in Iran.