Concrete, Asphalt 140 pounds/cubic footConcrete, Gravel 150 pounds/cubic footConcrete, Limestone w/Portland 148 pounds/cubic footCement, Portland 94 pounds/cubic footCement, mortar 135 pounds/cubic footCement, slurry 90 pounds/cubic foot
First, cement is the calcium sulfate binder which (with the addition of water and admixtures) becomes concrete for construction. Gravel for the construction of Hoover Dam was mined nearby, so the likely answer from those given would be the second.
