By whatever name, the Eureka can be traced, with gaps, from Nevada northward through Idaho into western Canada along the British Columbia-Alberta boundary,[2][3] and southward to southeastern California,[2][4] a north-south extent of about 2,200 kilometres (1,400 mi).

[5] The Eureka and its correlatives are lenticular in cross-section: in Nevada and Utah the formation extends more than 300 kilometres (190 mi) east-west, thinning out in both directions from maxima along its axis of more than 150 metres (490 ft).

[3] Cliff-forming quartzite, the principle part of the Eureka, is composed of more than 99 percent quartz, which includes both the sand grains and the cement that binds them.

[6] Almost all of the constituent grains were determined to have originated in Canada, and were carried southward by currents along the eastern shore of the Paleozoic sea.

[2] This concept is supported by several lines of evidence: (1) the only plausible source of such a large volume of sand is in Canada at about 56° north latitude where Cambrian sandstone was exposed extensively in Ordovician time;[7] (2) the base of the formation decreases in age from north to south as determined by marine fossils in subjacent beds;[2][4] (3) the formation becomes finer grained from north to south apparently due to progressive abrasion of the grains along the way;[2] and (4) the radiometric age of constituent zircon grains points to a northern source.