The Center for Land Use Interpretation has conducted extensive research on sunken cities throughout the US. Here's the information they provided on Kennett:
Kennett, CA - Boomtown Sunk
Though the old mining town of Kennett was a faded relic of its boomtown self by the time it was flooded by Lake Shasta in 1944, it was still home to a hundred people. Like other “gold rush” towns in northern California, it was established for mining and prospecting in the region in the 1850s, though it wasn’t until a railroad camp was built in 1883, with over a thousand Chinese laborers, that the population began to rise substantially. Gold was discovered nearby the next year, and a post office came in 1886. The largest copper smelter on the west coast opened in 1905, and by 1911, 3,000 people lived in town. The hills around the town were exfoliated and denuded by the acid fumes from the smelter, and farmers in the valley 15 miles away began a suit against the company that operated the smelter, for destruction of their crops. The mines closed after the end of WWI, the smelter soon followed, and Kennett’s population fell over the next two decades. The town now rests beneath 400 feet of water, along with many of the region’s smelters, paint factories, and mines, and their surrounding despoiled soils.