From California Historical Landmarks:
The Pelton Water Wheel, first commercially manufactured here at George Allan's Foundry and Machine Works in 1879, was a major advancement in water power utilization and greatly advanced hard-rock mining. Its unique feature was a series of paired buckets, shaped like bowls of spoons and separated by a splitter, that divided the incoming water jets into two parts. By the late 1800s, the Pelton Wheels were providing energy to operate industrial machinery throughout the world. In 1888, Lester Pelton moved his business to San Francisco, but granted continuing manufacturing rights to Allan's Foundry, where the wheels were manufactured into the early 1900s.
The curved shape of the buckets allow the wheel to operate much more efficiently than earlier water wheels. In his patent application, Pelton wrote
In my invention I construct a wheel having a flat face, and upon this face I secure peculiar-shaped buckets which are adapted to receive the stream from the nozzle and divide it, so that the two parts of the stream are directed into the curved bottoms of the two halves of the bucket, and by means of the inclined or flaring sides the two streams are caused to react and escape smoothly at each side, so that the whole reactionary force of the water is utilized, and the water is discharged clear of the wheel and the following bucket.... This action of the water causes it to be delivered upon the wheel with the full force due to its momentum, and in passing through the curved bottom and up the inclined sides the reactionary force due to this change of direction is also added to the primary power to assist in driving the wheel.
Pelton wheels are still used today for hydropower generation.
The site is currently a cultural center with several Pelton wheels and other mining hardware on display on the grounds.