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.

In the lead photo of “The River Runs Dry—Creation Story Preserves Historical Memory” and the photo above, the blue indicates limestone, the yellow-orange denotes desert sand. (The region shown in the photo is outlined in red on the map.) Studying this satellite photo, El-Baz could easily detect a dried riverbed (today called Wadi Al-Batin) cutting through the limestone at top center and, apparently (but only apparently), petering out as it reached the sand. When he extended the line of the river across the sand dunes, as indicated in orange in the photo below, El-Baz noticed that the patterns of the desert’s sand dunes changed precisely when they crossed this line. To the right (southeast), the dunes appear pockmarked, to the left (northeast) they are striated. Sand patterns like these are created by the circulation of the air in the desert, which in turn is influenced by the topography. Thus, El-Baz realized that something beneath the sand was the source of the variations in the sand. He determined that the river ran underground here, along a fault line.

On El-Baz’s recommendation, a recent space shuttle mission probed the area with Shuttle Imaging Radar, which transmits radar waves to the ground and receives their echo. This method successfully detected subterranean river channels in the Sahara. He is awaiting their results.

Throughout the past several hundred thousand years, during wet periods (such as the one described in James Sauer’s article), the river, in places 3 miles wide, dragged granite and basalt from the Hijaz mountains and dumped the pebbles along its fan-shaped delta, which covered two-thirds of modern Kuwait and part of southern Iraq. In memory of the pebble-strewn region that led him to the channel, El-Baz christened his discovery the Kuwait River.