Silver Strand State Beach

This guide to Silver Strand State Beach in San Diego starts with a handful of sand that glitters enough to have given the seven-mile spit its name, and the mineral behind that shine, mica, thin flat flakes that lie like tiny mirrors among ordinary quartz and shell. It raises the real puzzle: this mica was never native to the beach it covers. You'll hear how geologists traced it toward mountain rock and a river far from here, and the current that has been moving it along the coast for decades. Scoop up a handful yourself and watch how it catches the light.