Michael Dahl 
Canyon of Giants [PDF ebook] 

Hoping to avoid the Alcatraz guards, Zak Nine and Erro decide to climb down into a deep canyon to hide. But soon the boys see some huge rock formations that move! Zak and Erro are quickly caught by the giant criminals that have been imprisoned in the deep gorge. Some of the giants want to hand the boys over to the Alcatraz guards to gain their own freedom. But a few giants would rather turn the boys into dinner! Will Zak and Erro outwit their captors and get away before becoming the giants’ next meal?