The Pacific lowlands extend about 75 kilometers inland from the Pacific coast. Most of the area is flat, except for a line of young volcanoes, many of which are still active, running between the Golfo de Fonseca and Lago de Nicaragua. These peaks lie just west of a large crustal fracture or structural rift that forms a long, narrow depression passing southeast across the isthmus from the Golfo de Fonseca to the Río San Juan.