penstock pipes which will carry water from the reservoir through the dam and into the turbines in the powerplant. GENERAL Q. What are the numerous black spots above the tunnel portals and elsewhere? A. These are 8-inch square metal plates on the ends of anchor bolts. The anchor bolts extend into the rock to support the relatively thin outer layers of rock. Q. What are the white markings on the canyon walls? A. Survey control or reference points which have been painted on the rock. Q. Why was the small suspension footbridge built? A. More than 2 years was required to build the Glen Canyon Bridge—the highest steel-arch bridge in the world. Therefore, the footbridge was built so workers could cross the 1200-foot wide canyon; otherwise, it was 200 miles around by road. CONCRETE PLACEMENT GENERAL Q. How much concrete will the dam contain? A. There will be more than 5,000,000 cubic yards of mass concrete in the dam, and about 400,000 additional cubic yards in the powerhouse, tunnels, and other structures at the damsite. AGGREGATE (Sand and gravel for the concrete) Q. Where does the aggregate used to make concrete come from? A. From the streambed of Wahweap Creek, 6 miles from the damsite. Q. Is there a conveyor belt from the aggregate plant to the damsite? A. No. The aggregate is hauled in large bottom-dump trucks. CEMENT Q. How much cement will be needed? A. Approximately 3 million barrels, or 12,000,000 sacks. Q. Where does the cement come from? A. From a new cement plant constructed by the American Cement Corporation near Clarkdale, Arizona, 188 miles south of the damsite. POZZOLAN Q. What is pozzolan? A. Pozzolan is a cement-like material which occurs in natural deposits. Q. Why is pozzolan used? A. Pozzolan is cheaper than cement; it reduces shrinkage in concrete and develops less heat in concrete during the curing period. Q. Where is it obtained? A. Near Flagstaff, Arizona, about 115 miles from the damsite. About 220,000 tons will be used along with 564,000 tons (3,000,000 barrels) of cement. CONCRETE MIXING PLANT Q. What is capacity of the mixing plant? A. The maximum capacity is 480 cubic yards per hour, which is mixed in six, 4-cubic yard concrete mixers. Q. How large is the mixing plant? A. It is 217 feet, or more than 20 stories, in height. HIGHLINE CABLEWAYS Q. What will the highlines do? A. Their main function is to carry the buckets of concrete from the batch plant to points of placement in the dam and powerplant. Q. What is the size and weight of the concrete buckets? A. 12 cubic yards. When filled, the buckets weigh 31 tons, 24 tons of which is the concrete carried in the buckets.