Tales & Trails of a Traveling Wiseguy

One of our guidebooks says, without citation, that Zim Zim is a misspelling of Zem Zem, a sacred well in the city of Mecca. The author says it was the name given to the falls and the creek in the 1860s when a settler found it and exclaimed, "It's like the waters of Zem Zem!" (or whatever the 1860s linguistic equivalent was).

As for historical evidence of the name, a quick search turned up an interesting page from the Napa County Historical Society. It shows an 1876 map marked with "Zem Zem" and describes an autobiographical manuscript which gives a similar account of the name. Quite possibly this is the source the authors of the hiking guidebook found.