If you're managing a somewhat long-term project, it's best to at least attempt to keep some continuity between field people. Otherwise, you end up with these phone calls when you're out in the field:
Short Geologist (SG): "Hello?"
male voice: "Ok, I'm on Flibbergidget Street."
(long pause while SG tries to figure out why Flibbergidget Street sounds familiar)
SG: "Are you...making a delivery?"
male voice (exasperated): "Yeah, like I said, I'm waiting on Flibbergidget Street. They told me to go this way, but I've got a [very large piece of equipment] and the gate is locked and I can't turn around."
SG:...(light dawns) "Oh! You're delivering the [very large piece of equipment] to Site X! I'm actually 200 miles away, on an unrelated site, but I think I know who your contact person should be. I'll call him and let him know you're waiting, but here's his number for future reference."
...three days pass...the phone rings again, right in the middle of some new field crisis...
different voice: "Hi, I'm on Flibbergidget Street with [another piece of equipment]. I'm stuck outside the gate."
SG: "For the last time (something crashes in the background), I am no longer the contact for Site X. Call this number."
different voice: "Well, I tried that number, but the guy said he's not working at that site and doesn't have time for this."
SG: "Ok, what you need to do is..."
Two months later, guess who was back at Site X? No wonder the contractors got fed up.