A generalized reconstruction of Paleo-Bell River drainage and evolution of other major rivers in western and northern North America, after James Sears and others. By the Miocene, the Paleo-Bell River Basin reached its greatest extent. Rifts like the Rio Grande and Great Basin created an ancestral Colorado River that was yet to establish a course to the Pacific (location 1). Instead, it flowed north from the Grand Canyon region through structurally controlled valleys and into the larger Paleo-Bell River Basin via an ancestral Yellowstone River, whose gravels cap the Cypress Hills. This route was blocked by eruptions of lava in the Snake River Plain (location 2) associated with the Yellowstone Hot Spot. Repeated glaciation starting about 2.6 million years ago diverted north-flowing rivers like the Paleo-Yellowstone along ice sheet margins (location 3) to form the Missouri River. The ice sheets also disrupted the Paleo-Bell River Basin, causing river sedimentation to cease in the Saglek Basin. The Mackenzie River Basin was created, leaving the Saskatchewan/Nelson River Basin as the last remnant of North America’s Amazon. Credit: K. Cantner, AGI and Lionel Jackson, based on Sears, GSA Today, 2013.
“The complex, unique geology of the Los Angeles Basin, with its interlocking and overlapping ridges and valleys, resulted in a wildly unpredictable river that often sent torrents of water tearing over its banks.
Not long after California became a state in 1851, the water needs of a booming population stressed the Los Angeles River to its breaking point. Meanwhile, the fitful river endangered the settlements multiplying throughout the floodplain. After catastrophic floods in 1914, 1934, and 1938, the city, at the recommendation of the U.S. Army Corps of Engineers, agreed to straighten the riverbed and pave it with concrete, deracinating whatever plant and animal wildlife was left. A complex of aqueducts, dams, and reservoirs was built to import most of the city’s water; today, it delivers about 430 million gallons daily.”
Restoration of this watershed is a priority to many who live in and around LA.
“Now, as global warming steadily melts glaciers and polar ice sheets, quickening the pace of sea level rise, scientists say that a severe shortage of river-borne sediment — most of it trapped behind dams — will increasingly be felt along the world’s coasts.”
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“The first thing that struck me about this animal is the incredible robustness of the limb bones,” said McPhee, lead study author. “It was of similar size to the gigantic sauropod dinosaurs, but whereas the arms and legs of those animals are typically quite slender, Ledumahadi’s are incredibly thick.”