Ellensburg Blue agate

Sky-blue agate turns up in the windswept rangeland northwest of Ellensburg and, as far as anyone has found, nowhere else in the world. Most of it comes from around Reecer Creek and Green Canyon, with more near Thorp and west toward Cle Elum. The stones come out of the Teanaway Basalt, a reddish Eocene lava that in the agate fields is mixed with darker brown Columbia Plateau basalt from the Miocene. Nick Zentner, a geology lecturer at Central Washington University, thinks a river that no longer runs there carried them down Green Canyon and spread them across an alluvial fan. Geologists at the university suspect the colour comes from light refracted by tiny particles in the stone, the same reason the sky is blue, though more research is needed.

Native people knew the stones first. John Prentiss Thomson, whose father's jewellery store first promoted them, reported that local tribes passed them over for arrow tips but used them in trade with whites, and sheepherders reported the sky-blue rocks showing plainly on the hillsides. In March 1905 Austin Mires, an attorney who had been Ellensburg's first mayor, sent blue agates from the local beds to Seattle to be set into rings, and about a decade later he and his wife were cutting and polishing them at home. By May 1913 local Native people had shown the jeweller J. N. O. Thomson where to find them. Newspaper stories set off an agate-hunting fad among tourists that lasted through the 1940s.

Most of the ground has since gone private. HistoryLink reported in 2003 that virtually all of the original agate beds were on private land, many of them cultivated, and farmers occasionally turn up the stones while plowing. Hunters need a landowner's permission. The Daily Record described one fee-dig ranch, the Rock 'N' Tomahawk on Upper Green Canyon Road, where Bernice Best had sold $5 permits since 1994 and drew about 400 hunters a season between late March and August. The largest stone she had seen, found by a regular visitor in 2015, was about the size of a fist.

The Kittitas County Historical Museum, open since 1961, holds stones from thumbnail size up to ones that could double as a bookend, and its director, Sadie Thayer, has said the collection may be the largest in existence. The museum does not authenticate or appraise finds. House Bill 2757, which would replace petrified wood with Ellensburg Blue as the Washington state gem, passed the state House 91 to 7.