Photo from Flickr user oxcnpxo
Have you ever noticed a rotten egg-like sulphur smell in the San Miguel neighborhood of Walnut Creek, which includes John Muir hospital as well as Lime Ridge? It turns out that smell existed long before people even lived there due to sulphur springs and minerals in the area. KQED has an interesting article here explaining the details. This quote comes from a 1915 US Geological Survey:
“A group of sulphur springs lies near the northeastern base of a low ridge about 2 miles northeast of the town of Walnut Creek. The largest spring is on the ridge about 100 yards from its eastern base and 25 yards north of the county road [Ygnacio Valley Road]. When the place was visited, the water rose in a board-curbed pool protected by a latticed house and was piped to a cattle trough a few yards away. It yielded about 3 gallons a minute of mildly sulphureted water, 81° in temperature. . . . Five other smaller springs issue in a belt extending 350 yards along the base of the ridge, in and near the barnyard of Sulphur Springs farm. Two of them have been piped to watering troughs near by. The other three are of seeping flow and form only small marshy places.”