On the banks of the Santa Ana River -- at nearly 100 miles, the longest in Southern California -- the interplay between nature and culture becomes visible. Since the first humans arrived in Southern California several millennia ago, people have maintained a complicated relationship with the Santa Ana River, accepting its life-giving water but fearing its wrath. The Santa Ana shaped settlement patterns and land use at the same time that people drastically reshaped the river.
Today, like the region's other watercourses, the Santa Ana River bears little resemblance to its wilder, historical self. But -- despite being tamed by two massive dams and confined for much of its course to a concrete flood control channel -- the river remains one of the most important natural features of the Southern California landscape.
Rising in Southern California's Transverse Ranges, the Santa Ana is an ancient river; geologists suspect that the river's course predates the uplift of the Santa Ana Mountains, which the river cuts straight through at Santa Ana Canyon. Over millions of years, fed by infrequent but reliably intense storms, the river has carried sediment from the mountains and deposited on the shore, slowly forming a coastal plain that today is home to millions of suburbanites.