A colonial-era stone façade stretches along a sunlit cobblestone street in San Juan del Río, Querétaro — its massive carved cantera blocks, ornate window grilles, and weathered wooden doorway speaking to centuries of provincial Mexican craftsmanship — and inside this very building, a traveler bought something special: a handwritten note on the back simply reads "Bought stones here," referring to the opals and semi-precious gems sold at La Guadalupana, a gem dealer whose contact information is printed on the reverse. San Juan del Río sits at the heart of Mexico's famous opal-mining region, and La Guadalupana (Tel. 1-03, 16 de Septiembre #5) was evidently a well-established stop on the tourist circuit by October 19, 1972 — the date penciled on the back. The card was produced by Mexfotocolor (catalog no. 3194-C, printed in Mexico) and serves double duty as both a souvenir postcard and a business card for the gem shop.