How to Find a River—No Divining Rod Needed

Most people think little about pebbles, unless they’re in their shoes, in which case that’s probably all they think about. But for geologists, pebbles provide important, easily attained clues to an area’s geologic composition and history. The pebbles of Kuwait offered Boston University scientist Farouk El-Baz (right) his first humble clue to detecting a river, identified in the accompanying article as the Pishon, that once flowed softly across the now-desiccated Arabian Peninsula.

Geologists had long realized that pebbles of granite and basalt are abundant throughout Kuwait, even though these rocks are not indigenous to the area. The nearest rich source lies in the Hijaz Mountains, about 650 miles to the west, in Saudi Arabia. Trying to understand how the pebbles reached Kuwait, El-Baz examined photos of the region taken by satellites orbiting the earth.