Crystal Peak

Thanks, Andy! No, "tuff" and "tufa" are two completely different rock types--with unfortunately very similar names! A tuff is an igneous rock, formed from particles of lava. They range all the way from water-laid tuffs--"igneous sandstones," essentially, to so-called "welded tuffs" ("ignimbrite" is the $64 word), which consisted of molten particles entrained in hot gas that stuck together when they settled out to yield a rock that looks just like a lava. The Tunnel Spring Tuff is a welded tuff, and they're a common product of what today is called a supervolcano.

A tufa, OTOH, is a freshwater limestone, commonly deposited around calcium-rich springs, but they can also be deposited by wave action along the shores of freshwater lakes high in dissolved calcium. (What happens is that CO2 exsolves from the agitated water, which causes precipitation of calcium carbonate.) Both types are common in my area and are associated with Pleistocene Lake Lahontan. Here are some tufa "towers," deposited from springs:
www.ipernity.com/doc/289859/41889102/in/album/893866
and here are some shoreline tufas (plus my Jeep's aerial!) near Pyramid Lake, on the eponymous reservation:
www.ipernity.com/doc/289859/23564783/in/album/452889

The rock that _is_ basically the same as tufa is travertine, also a freshwater limestone. That term is commonly used for deposits in streams, but it's also used for springs, and the distinction gets a bit arbitrary (and historical!)