<div class="description">
<ul><li><b>Scope and content:</b>  Photograph from Volume Two of a series of photo albums documenting the construction of Hoover Dam, Boulder City, Nevada.  Full caption of photo reads:</li></ul>
"Concrete gun carriage used in placing 110 degree top-arch concrete in diversion tunnels. Concrete is hauled by truck in dump-buckets into position under carriage, hoisted to upper deck by bridge crane operating over head, dumped into hoppers and compelled into forms by compressed air through two 8-inch steel and rubber pipes. Two gun units are operated, one from either side of deck. The entire assembly consists of three major units: the concrete gun carriage seen in the photograph, a traveler carriage used to support the compressed air pipes between the gun carriage and the form and the form carriage itself. All three units operate over rails placed on tunnel alignment. The form carriage is given flexibility for curve construction through a system of gores and wedges. See also following photographs."</div>
<div class="fn value">
Unknown author<span style="display: none;">Unknown author</span> or not provided</div>
<a href="https://en.wikipedia.org/wiki/U.S._National_Archives_and_Records_Administration" class="extiw" title="en:U.S. National Archives and Records Administration">U.S. National Archives and Records Administration</a>