VALLEY of DEATH (Mysteries in Our National Parks) by Skurzynski, Gloria; Ferguson, Alane

What's causing the deaths of desert bighorn sheep in Death Valley National Park?

Wildlife veterinarian Olivia Landon has been called in to investigate. The plot thickens when her daughter, Ashley, is kidnapped by militants who mistake her for Leesa, a mysterious girl temporarily in the Landons? care. Tension builds to a spine-chilling climax when a showdown in the desert leads the family to a missile testing site and the key to what is killing the sheep. 

From National Geographic