THE ORIGIN AND EARLY HISTORY OF LAKE MERRITT, OAKLAND

Lake Merritt has a long and complex history involving geology, oceanography, biology, and human activities. During the Pleistocene, Milankovith cycling caused sea level variations below the present level that was exceeded only twice. During lower sea levels, San Francisco Bay was a river valley and Merritt Canyon, site of the future Lake Merritt, was an eroded stream valley. About 125,000 years ago, the sea rose 8 m higher than it is now. It left erosional and depositional evidence along San Francisco Bay and over and around the site of Lake Merritt. From 13,000 to 4,000 years ago, sea level also rose again from 120m to its present height. The shoreline 13,000 years ago lay 50 km off the Golden Gate near the Farallon Islands. At this time, people from Asia crossed the Bering Land Bridge and spread south to California. The ocean reached the Golden Gate ~8,000 years ago and at ~4,000 years ago, filled the bay and the mouth of Merritt Canyon creating San Antonio Slough with tidal mudflats and marshes. Ohlone people occupied the bay area and the slough in Merritt Canyon. They built 425 shell mounds around the bay with six near the slough. In 1770, Spanish arrived and built missions, forcing the Ohlone into them. Luis Peralta was granted 44,800 acres including San Antonio Slough as Mexico gained independence from Spain in 1821. After the Mexican American War in 1848 and gold discovery in the Sierra Nevada, Americans and others rushed to the mountains. Most found nothing and returned to the Bay Area, some residing in Oakland. Americans subdivided Peralta’s land, building homes around San Antonio Slough. The city dumped its sewage in the slough that already smelled bad due to the mud and marshes. Mayor Samuel Merritt dammed the channel in1868-1869, so water covered the slough at high tide and was retained at low tide, thus damping the smell and creating an attractive estuarine lake, soon called Merritt’s Lake and later Lake Merritt. Birds were hunted along the shore causing damage to homes, so Merritt had the state legislature declare Lake Merritt a nature reserve, the first in the nation. As an estuary, the lake at times experiences low oxygen, algal blooms and fish kills. Future sea level rise is expected to inundate the lake and surrounding land.