Just bring a high meele doed on the city at extinction and hit the lamp post for dust. Each 1000 dusts give 1 element. Do take note you can't transfer element, so if you're not from extinction, upload the dust and craft the element on your base.
Take a 100% afinity giga and some velo on turret mode to complete the element nodes on extinction. Careful not to bite the big node with the giga as it take lots of damage and it's the only way to fail if you do like this (bring a good shotgun at leave the dinos hitting the node to kill with the shoty). After completed use a Mantis with high meele and good pick to harvest the node (if you're not on extinction, put the element on the terminals and make it turn dust to transfer out)
Extinction is a very gud map for ele but if ur on ci u can go to the elderich isles and hit the small blue crystals for ele shards blue green and red gems and some crystal. Mining drill does not work on these. Theyre usually next to some bigger darker blue crystals.