SDFD was called to the preserve, located between the neighborhoods of Rancho Penasquitos and Sorrento Hills, just before 11:30 a.m.
The unidentified man was suffering from dizziness, fatigue and nausea — all signs of dehydration, said Jose Ysea, SDFD spokesman.
“This is the worst time of the day to be out hiking and walking,” Ysea said, in reference to time frame for the open-space rescue.
Ysea said first responders airlifted the man to Elizabeth Rabbitt Park where he received a medical evaluation, but then refused further treatment. All first responder units were cleared at 12:30 p.m., he added.
City News Service contributed to this article.