At 9.30pm on 23 July 2018, the second wave of runners lined up at Badwater Basin in Death Valley, 280 feet below sea level. The heat from the day had not cooled and the temperature was 118F (48C), even though the sun had long since gone down.
To make matters worse, it was abnormally humid for the California desert. Sixty-two-year-old Pamela Chapman-Markle looked down the line of racers, recognizing about half the competitors from previous years.
On a normal day she would be heading to bed in a half hour, and although her heart was racing with anticipation, she was already tired, acutely aware that she was about to miss two nights of sleep.