this construction on hoover dam in 1931. the project employed over 21,000 workers. , one of the largest man-made structures in the world when it opened in 1936. it was completed two years ahead of schedule. next, 1955 department of the interior film about the planning and the building of hoover dam. the story explains the engineering feat necessary for construction and promotes economic and recreational benefits provided by the structure. ♪ >> in 1930, president herbert hoover, for whom the dam is named, signed the bill to get it started. there was a combine of six major construction firms and men and machines went to work to build this dam of on presidents its size. a modern civil engineering wonder. reclamation engineers rushed to completion specifications and design drawings. the dam site completed their surveys and investigations. the thunder of man's determination to dock or the colorado river reverberated canyon the sheer black is construction got underway. the first major task was to divert the river around the dam site area to do this, for tunnels, two on each side were drilled through the canyon walls. crews at the dam site completed their surveys and investigations. the thunder of man's determination to conquer the colorado river paraded between black canyon as construction got underway. the first major task was to divert river around the dam site. four tunnels were drilled to the canyon walls. each 56 feet in diameter, they averaged 4000 feet in length. drilled holes were packed with dynamite and plaster. workman excavated over 1.5 million cubic yards of blasted material in 13 months. the tunnels were lined with concrete three feet thick. explosions rocked the canyon daily before placing the concrete and the dam began. acrobatic workman prepared the canyon walls for each blast. they were called high scalars. suspended on ropes, they drilled holes in the rock and loaded them with dynamite. after each explosion, these daredevils prying loose rock and clearing the walls of debris. in november 1932, the colorado river was diverted. under control for the first time in its history, the river float around and past the site. men in trucks dumped the rock embankment. across the canyon. below the tunnel openings, forcing the river from its age-old bed through the huge divergent tubes. a second earth and rock dam was built across the river above the tunnel outlets downstream. keeping water from backing into the foundation area. isolated and protected from the river, the site was pumped dry. man and machines dug 135 feet the low the old river level to reach bedrock. for the dam's foundation. excavating over 2 million cubic yards of rock and sand. as cleanup of the site expose the ancient bad of the colorado -- a bed of the colorado river river, geologists read the , history of what happened ages ago. workman cleaned and prepared bad rock services to receive the first concrete. 12 miles upstream, drag lines, excavated sand and gravel. concrete was dispatched to all areas of construction. nine cable ways lower the concrete into the forms and handled other supplies and equipment as well. as the first bucket of concrete settled into its foundation on june 6, 1933, hoover dam began its rise from the depths of black canyon. as cable ways dropped load after load of concrete, dam soon reached its thickness in its base. the interlocking columns skyward as crew set new records daily. bucketful after bucketful ran a continuous cycle dumping its load of 16 tons. it was truly a modern engineering wonder. crews vibrated and compacted >> the c-span cities tour takes book tv and american history tv on the road traveling to u.s. cities to learn about their literary life. this weekend, we partnered with comcast for a visit to st. paul, minnesota. >> st. paul in the 1930's, i would not call it las vegas, but it was a very lively city because the gangsters brought their gun molls. during prohibition, you had the biggest jazz artists of the decade here in st. paul. it was a very lively place, partially because the gangsters were welcome here. virtually every major gangster, kidnapper, and bank robber in america lived and worked within a three block radius of where we are standing today. john dillinger, they be faced carpus.alvin "creepy" people don't know that because there's no statues of these gangsters but this was the epicenter of 1930's crime in the era of john dillinger. the federal bureau of investing haitian under j edgar hoover had -- the federal bureau of investigation under j edgar hoover had their center here. sent tongsters were other prisons across america. it's where it began and ended. we are standing here at historic looking over the junction of the minnesota mississippi rivers. st. paul is located up the mississippi river from port snelling and the fort was here before the city was but the fort is intimately connected in the creation of st. paul. in the 1830's, there were groups of settlers that were living on the military's property. finally, the army had had enough of competing with them for resources and they felt they should be removed officially from the military property. the settlers moved across the river to the other side and they formed what became the nucleus of the city of st. paul. when you think about the story and the history of this region, you think beyond the walls of fort snelling. that's what we try to do here is push people to think more about what it means when all of these cultures came together? what perspectives do they have on these historic events? >> watch all of our events from st. paul today at noon eastern on c-span two and sunday afternoon at 2:00 on american history tv on c-span3. with live coverage of the u.s. house on c-span and the senate on c-span two, here on c-span3, we complement that covers by showing you the most relevant congressional hearings and public affairs events. on weekends, c-span3 is the home to american history tv with programs that tell our nation's story including six unique series, the civil war 150 anniversary, visiting battlefields and t vance, american artifacts, during museums and historic sites to discover artifacts reveal about america's past and heckscher he -- and history bookshelf and the presidency looking at the policies and legacies of our nation's commanders in chief. lectures in history, with top college professor delving into america's past and our new series, reel america featuring archival films from the 19 raised through the 70's. c-span3 -- created by the local -- by the cable tv industry. watch us on tv, follow us on facebook and twitter. >> each week, american artifacts takes viewers into archives, museums, and historic sites around the country. next, we visit fort mchenry national monument and historic shrine in baltimore to learn about the birth of the "star spangled banner."

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