One of the most popular pieces of equipment used during gold rush times in XIX century was a rocker box, sometimes called a cradle.
Collier's New Encyclopedia from 1921 defines this device as a mechanical contrivance used in placer mining, consisting of a box on rockers and moved by hand, used for washing out the gold-bearing soil.
Rocker allowed to separate gold and other heavy elements from sand and gravel by shaking and rocking the high-sided box, open on one end and top. The whole box was placed on rockers and equipped with classifier sieves screening-out larger pieces of rock and other material, allowing only finer material through. Screens were usually with half to one inch openings where clay and clods of soil could be broken to smaller parts. Between the sieve and the lower sluice section was a baffle, which acted as another trap for fine gold. Like a sluice box, the cradle has riffles and a carpet for trapping the gold.
Rocker, probably invented by Cornish miners, was one of the tools used to easily extract gold from rocks and riverbeds during the California Gold Rush. Isaac Humphrey, generally known as "Major" is said to have introduced the rocker to the California gold fields. Sacramento was a real testing ground for prospectors and miners, from all over the world, who carried out this knowledge and experience to next gold rush camps.
Lots of early California miners, later called 49ers, spreaded out this gold fever and started new rushes along all North American west coast up to Alaska, in Australia or New Zealand. First Australian rocker, for instance, was made by William Tom Jr following directions from Edward Hargraves and was based on similar cradles used to wash for gold in California.
The rocker box is not so popular hand mining tool anymore, but still can compete with a sluice box in some areas. Cradle has got a big advantage in areas where is not enough water to supply the sluice box. Handling the rocker requires attention and precision from the gold prospector, but skillfully operated allows to wash over twice as much material as a normal pan (1-3 cubic yards can be washed per man-shift).