“69 kV”
Small voltage as transmission lines go.
Yes, 69kV is the lowest transmission voltage in AZ, but also the highest voltage that can/should be put underground. 115kV, 230 kV and 500kV lines cannot safely nor cost effectively be put underground. The intense heat buildup in the energized ug cables, conduit and encased duct bank are virtually impossible to manage, and the costs to do so would be ridiculously high.