These drawings represent only a small portion of Porter's output, but they range over a variety of subjects from his California period, beginning in 1928. The works have been divided into series and subseries; for example, building designs for Caltech are further subdivided for individual structures. Highlights of the collection include original design proposals for the 200-inch telescope mount, in both schematic and three-dimensional/cutaway form, plus a series of drawing of Hale's spectrohelioscope. Some of Porter's military drawings are also represented, as well as miscellaneous drawings of Caltech engineering projects such as the Hydrodynamics Laboratory. Many of the drawings have been reproduced and scanned into the Caltech Archives' picture database, PhotoNet, which is searchable from the Archives' website.