 After 1075, construction consisted of minor additions and alternations, with the exception of a row of three large, Chaco-style second- and third-story round rooms that were added to the plaza-facing center of the main room block during 1075–95.Much of the later construction, including the large Chaco-style kivas, was in McElmo style masonry, using shaped blocks of relatively soft tan colored sandstone instead of the previously preferred harder, denser dark brown sandstone, which may have been quarried out in the central canyon after 1075.Chetro Ketl required an estimated 50 million sandstone blocks and more than 500,000 man-hours to complete.