(See previous post for context)
The manual technique: Find the taproot. Begins with clipping and sawing, generally ends in a hole ten feet over and seven feet down from where you thought the tree was. This is not feasible on a large scale. At the end of the day, your volunteers will require quantities of beer hard to provide in a wilderness setting, even with raft support.
Cut stump treatment is another possibility, which involves sawing off the limbs and painting an herbicidal glue onto the stumps. A lot easier than digging them out, but it leaves a lot of pointy sticks around and is still not feasible on the scale of canyon country. The Bosque del Apache refuge in New Mexico bulldozed, burned and poisoned cyclically for years before they finally got the bastards under control, and they had road access. You see why beetles start to look more appealing.
A spawning bed for native fish, mercifully pristine. But Tamara and her volunteers cleaned out the lower end of it this June. And the tamarisk are lurking not far away.