The head of one stream gets grafted onto the stem of another stream, and the transportation of sediment from hill to bay - the basic function of streams - is stymied and randomized. Streams get stretched and snap, interrupting their natural evolution into well-organized networks like Merritt Creek’s. Headwaters in the hills get slowly cut off from their downstream reaches. Briefly, the fault messes with streams as its sides slip past each other. This is an intricate subject I plan to address in future posts as well as my book. Third, unlike Oakland’s other major streams, Merritt Creek’s watershed didn’t cross the Hayward fault and was not affected by it. I argue that this substrate didn’t generate as much mud or clay as its neighbors and made the stream network less prone to clogging. Second, Merritt Creek drained a large area of hard bedrock: the Franciscan sandstone, shown in blue on the geologic map, that underlies the hills of Piedmont. It was better equipped to cut into the exposed floor of the Bay. Whereas those creeks spread out their floodwaters on the plain and slowed their flows (depositing their sediment across the landscape), Merritt Creek was confined between elevated banks and couldn’t slow down. It didn’t dribble across a wide coastal plain like Temescal and Sausal Creeks on either side. And as the watershed map shows, the stream network is well organized, capable of delivering stormwater in a big flush. I can cite three reasons for that.įirst, Merritt Creek had the largest watershed between San Pablo and San Leandro, thus it had the greatest water-gathering power in the area - especially during glacial times. My argument is that Merritt Creek is a drowned valley today, instead of an ordinary creek like the rest of Oakland’s streams, because it cut down deeper than other creeks. Here they all are on the watershed maps from the Alameda Country Flood Control District.Īnd if you adjust this map in your mind by subtracting the sea, Merritt Creek also received input from 14th Avenue and 23rd Avenue Creeks (that is, the rest of San Antonio Creek). Three more smaller streams also drained into Merritt Creek: “Kaiser Creek” at 20th Street, “Adams Point Creek” at Perkins Street and Park Boulevard Creek at the E. The late Pleistocene creatures and vegetation there I will leave to your imagination. You know, let’s call the drowned valley Pleasant Valley, because it surely was one. The eastern arm of today’s lake was where three creeks joined: Pleasant Valley, Wildwood and Indian Gulch (Trestle Glen) Creeks. Glen Echo Creek ran into Merritt Creek down a swale where the north arm of Lake Merritt sits today. Today’s Lake Merritt, then, is a drowned stream valley - a term east coast geologists know well, but seldom used around here.įor clarity’s sake I will use the name Merritt Creek for the stream that occupied that valley during glacial times. Except for the Golden Gate itself, the whole Bay was dry land, and all of our creeks ran out far beyond today’s shoreline to join the combined Sacramento-San Joaquin River. When the ice caps were at their largest, the sea sat hundreds of feet lower than today. My theory starts with taking the mind back into recent geologic history - the dozens of ice ages that have occurred regularly for the last 2-plus million years. but if you look for it, for instance down 10th Street past the museum and auditorium, you can get a sense of its original width. Later the mouth got filled in leaving the narrow passage we know today. Small craft could use it when the tide was high, and duck hunters were a common presence there, but for serious commerce it was useless, and Oakland’s landing at the foot of Broadway was little better.īack then, San Antonio Slough had a wider mouth lined with wetlands, with terraces roughly 25 feet high on either side. The slough extending to the north - today’s Lake Merritt - had strong tidal currents and a very shallow mouth. It had a central channel, just a couple hundred yards wide, that was deep enough for ships, and the rest was tidal mudflats or treacherous shallows. “San Antonio Creek” was the inlet that led to the existing landing at Brooklyn. It’s a fat 1200-pixel image worth zooming in on (or study the full-size scan from Wikipedia). It covers the same area as the Google Earth clip above. This is an excerpt from the “Bache map” of 1857, a survey of the waters surrounding the newborn city of Oakland and its neighboring town of Brooklyn painstakingly made by the U.S. and think of Oakland as it originally existed. I have a theory, based on the last million years or so of geologic history plus some of the latest research.įirst of all, we need to ignore the Lake Merritt we know today: Then it has Lake Merritt, formerly known as San Antonio Slough - an arm of the sea extending more than a mile inland from the shore. Oakland has several major, permanent streams crossing it from the hills to the Bay.
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