Answer
Water will boil at a higher than normal temperature in Death Valley because there is more air pressure on the water molecules.
Step-by-step explanation
The boiling point of water, or any liquid, varies according to the surrounding atmospheric pressure.
Water boils at a lower temperature on top of a mountain because there is less air pressure on the molecules. This means the higher the pressure, the higher the boiling point of water. At low pressure, the boiling point of water comes down. The boiling takes place at a lower temperature at the top of a mountain due to low pressure.
Therefore, at altitudes below sea level, water will boil at a higher temperature; the lower you go the higher the boiling point. The higher you go the lower the boiling point