The north coast karst

The north coast of Puerto Rico is a belt of tropical karst developed over thick Oligocene and Miocene limestones. The Geological Survey's Professional Paper 899 by Watson Monroe, 1976, is the monograph of the landforms. Later Survey work on hydrogeology maps the same rocks as the north coast limestone aquifer system. Mogotes — steep residual hills — sinkholes, cockpits, caves, and disappearing streams are the furniture of that belt from the northwest to the edge of San Juan.

Mogote: an isolated, steep limestone hill. The word is Spanish in local use and technical in the Survey's papers.

Karst is not a park. It is a water system with holes. Contaminants travel. The quarry takes hills. Housing and industry sit on a surface that can swallow a road. The Arecibo radio telescope famously occupied a sinkhole between mogotes; that is an illustration, not the claim that geology is a monument. The aquifer withdrawals the Survey has published are the practical record: public supply and industry drinking from a limestone sponge.

The Cordillera is volcanic and differently sedimentary; the south coast is a drier alluvial plain with its own aquifer. Melting that into a single "island geology" paragraph erases the reason the north looks like a basket of green cones and the south looks like cane and scrub. Climate and rock write the map together. This page is the rock.

1980 on the date line is a convenience near the Survey's karst decade, not a year of discovery. Monroe is 1976. Giusti's hydrogeology paper is 1978. A 2010 karst map compiles the contours. The landforms are older than all the reports. The reports are what we can cite without inventing the height of a hill.

Karst is stone and water, not a weekly ramp of drought colors.

Drive the north and the mogotes repeat until they don't. That end is the edge of the limestone, not a metaphor. If a housing essay needs a flood route, it can take a river that crossed this karst and then left it. The stone remains, full of holes.

Sources: USGS Professional Paper 899, The karst landforms of Puerto Rico (Monroe, 1976). Freeze 2026-08-22.