In a 1984 article, Mill Valley historian Henri Bussy wrote, “One of the commercial ventures of Mill Valley was a gratuitous one. Around 1891, a sulphur spring was discovered in the fields on the site of Old Mill School. By 1895 a gazebo had been built over it and people came from the entire bay area to benefit from its waters, which, with their odor of rotten eggs, were believed somehow to be curative.” Attempts to market the spring water for medicinal powers produced only a limited commercial success. By 1904, the gazebo was in need of repair, detritus clogged the water and the sulphur spring was uninviting to Mill Valley people. But in 1905, the water of the long neglected sulphur spring was once more made available for a social at the Congregational church thanks to the good work of the Outdoor Art Club. The block of land boarded by Throckmorton, Elma, Lovell and Old Mill came to be known as the Sulphur Spring block. In 1918, the school district purchased the block, bought the six houses on it and moved them up Throckmorton Ave. The spring has bubbled through the school grounds over the years, most recently during the renovation work of 1995-1996.