Drilling rig masts and methods of assembly and erection

A system for erecting a drilling rig mast, the system comprising:

• a substructure comprising a mast connection, a first substructure subassembly, and a second substructure subassembly that is adapted to be positioned laterally adjacent to and spaced apart from said first substructure subassembly so as to define an open area therebetween and an opening between adjacent ends thereof, said open area being adapted to at least partially receive a wheeled mast moving apparatus that is used to move a mast section through said opening and adjacent to said mast connection;
• a bottom mast section comprising a first connection apparatus positioned at an upper end thereof and a bottom connection apparatus positioned at a lower end thereof, said bottom connection apparatus being adapted to be pivotably connected to said mast connection, wherein said bottom mast section is adapted to be moved through said opening and positioned at least partially within said open area;
• and
• a second mast section comprising a second connection apparatus positioned at a lower end thereof, wherein said first connection apparatus is adapted to engage with and be removably connected to said second connection apparatus when said bottom mast section is pivotably rotated about said mast connection.