Just as we were ready to leave and return to camp we took off our hats, and then overlooking the scene of so much trial, suffering and death spoke the thought uppermost saying:—“Good bye Death Valley!” then faced away and made our steps toward camp. Even after this in speaking of this long and narrow valley over which we had crossed into its nearly central part, and on the edge of which the lone camp was made, for so many days, it was called Death Valley.
Source: wiktionary