Peach Bottom roofing slate was discovered about 1734 on the ridge where Delta, Cardiff, and Whiteford are now located by two Welsh pioneer farmers, William and James Rees, who roofed their buildings with crude slates in the first use of native roofing slate in America. The first actual quarry opened about 1785 as the first commercial slate quarry in the United States, but it was not successful because transportation was difficult, with few roads and very heavy slate, and because skilled slate workers were lacking. In 1840, the opening of the Susquehanna and Tidewater Canal along the west bank of the Susquehanna River solved the transportation problem and opened many new markets for roofing slate. In 1845, the first Welsh slaters came to the area with the knowledge and skills to turn the rock into a marketable roofing material, and new quarry operations opened. Hundreds of workers, mostly from Wales, worked in as many as twenty quarries, and in 1851 Rowland Parry of Peach Bottom exhibited slate samples at the London Crystal Palace Exhibition, where it won first prize as the finest roofing slate then known. Its reputation endured, and many slate roofs remained in the community as a lasting legacy.