Tannis wants you to go the preservation and find some experiment notes on Slag. The first one is just past the area with all of the Hyperion troops, right after falling off the bridge into another area with Skags. You’ll have to run up a broken pipe and through a small room. The notes are on a crate in that small room.

Go through the entire Wildlife Exploitation Preserve until you come to the rooms with the two Badass Skags. There is a small room with a red chest in it that you want to enter. The notes are in a cardboard box. Continue on to the third note’s location, which will require you to press a switch behind the greeter robot, revealing a hidden section right above it, with the notes.

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Most of the notes are in obvious places (left), but one will require you to push a button (right) to open up a secret safe with the note.

Keep going through the area as you normally did until you arrive in the big storage-like area with Hyperion enemies. Go up the stairs and you’ll see the marker pointing to a switch on the side of some cages. Pulling this switch will make a bunch of Stalkers come out, so kill them and look in the one cage to find the notes. Return to Tannis in Sanctuary to turn in the mission.