The main cellblock was built to house up to 204 prisoners, although the Superintendent's report stated that at times as many as 240 were kept there. Each cell was approximately 9 foot by 12 foot and could hold six prisoners, and when space became limited, the more trusted prisoners slept in the hallways. The cells were constructed of strap iron and granite rock that was plastered and whitewashed; the iron was shipped from California by steamboat, while prisoners quarried the granite on site. Originally, the cellblock was completely enclosed rather than exposed to the elements as it is today. One of the earliest electrical generating plants in the West supplied power for lights and a ventilation system there. In 1902, a hospital was built on top of the main cellblock, with a dispensary, doctor's office, operating room, attendant's room, bathroom with flushing toilets, and a consumptive ward. Prisoners from other institutions were also sometimes sent to the Territorial Prison at Yuma to recover their health.