The Pacific Overland Expo Auction, held April 22 and 23 of 2016, was billed as "The first annual Pacific Overland Expo horse drawn vehicle and equipment auction." It took place at the Yamhill County Fairgrounds in McMinnville, Oregon.
For these covers, the cachet consisted of a high-resolution photograph taken in the Oregon Cascades. Two triangular stagecoach stamps from Pacific '97 (Scott #3131) sit along the bottom edge, shifted to the left. Per my request, the pictorial postmark, in the shape of a horsedrawn wagon, is centered between the peaks of the triangles, tying both stamps to the cover.
A very simple cachet, but I like the effect a lot.