For the volcano in Washington state, USA see "Mount St. Helens".
Mount Saint Helena is a peak in the Mayacmas Mountains with flanks in Napa, Sonoma, and Lake counties in California, United States. Composed of uplifted 2.4 million year old volcanic rocks from the Clear Lake volcanic field, it is one of the few mountains in the San Francisco Bay Area to receive any snowfall during the winter.
The mountain has five peaks, arranged in a rough 'M' shape. The second tallest, immediately east of the main summit, is the highest point in Napa County.
Mount Saint Helena was originally named Mount Mayacamas but was changed after a Russian survey party ascended the peak in 1811 and left a copper plate on the summit inscribed with the date of their visit. The plate also contained the name of Princess Helena de Gagarin, wife of Count Rotscheff the commanding officer of Fort Ross.
Robert Louis Stevenson and Fanny Vandegrift Osbourne spent the summer of 1880 honeymooning in an abandoned mining camp on Mount Saint Helena. Stevenson's book The Silverado Squatters includes his experiences while living there.
The peak is reachable by hiking trails leading from Robert Louis Stevenson State Park.
The headwaters of the Napa River are on the southeast slope of Mount Saint Helena.