Underneath the lake lies evidence of the dams construction. The steps on this panel and the next one show how hands and hooves toiled to complete this engineering feat in 1892.
The rest of this marker consists of three illustration accompanied by captions. They captions are presented here, left to right. Click on the image to enlarge it.
Clearing the area:
Workers "grubbed" (removed) 333 acres of brush and trees from the area to be flooded, to ensure rotting vegetation would not affect the quality of the reservoir's water.
Tunnel No. 1:
In 1874, laborers dug a spillway tunnel through the rocky hillside to divert San Leandro Creek while constructing the dam. Tunnel No. 1 was originally 30 feet above the canyon floor and later delivered water to homes.
Digging the dam:
To prevent leakage and the creeks' return, laborers dug three trenches nesting one inside the other. The largest ditch was 900 feet by 150 feet; the second ditch or "puddlepit" was 90 feet from bank to bank and about 140 feet long creek-wise. In the third ditch, laborers constructed three concrete walls and then sealed the trench with concrete grout.
Puddling and compacting:
Laborers spread clay and choice materials obtained from adjacent areas to fill the two larger trenches. Water from a stream pump kept the clay wet and workable, and would form puddles giving the second ditch, puddle-pit, its name. Laborers drove gangs of horses across the puddle-pit to compact the layers and create a water resistant surface.
"Historians say Chabot was watching some cattle trample across a muddy creek bottom when he got the idea for the primordial impacting plan."
Oakland Tribune June 9, 1968.