"Great river—greater dam." 

In standard Abbey-style deadpan humor, Abbey introduces a symbol of the  protagonists' enemy: the bridge spanning Glen Canyon and the Colorado     River. This bridge, which the gang sabotages, and its adjacent dam represent the kind of industrialization of the Southwest against which the  gang fights. 

"Someone or something was changing things." 

Hayduke, upon returning to the Southwest for the first time in years, notices drastic changes to the landscape. Like Doc, Hayduke seems to characterize the forces of industrialization not as individual humans but as a machine.

"Though still a lover of chipmunks, robins and girls, he had also learned like others to acquire a taste for methodical, comprehensive and precisely gauged destruction." 

Whether Hayduke had a choice in acquiring his taste for the kind of  firearms- and explosives-based destruction he learned in Vietnam is unclear. His appetite for these things stands at odds with the less-violent tendencies of the rest of the gang.