Tommy's Dam - Hydroelectric Dam
Comic #7: Foreign Element
As you make your way down the slope, hang to the right. A little before passing under the bridge, you can actually ascend a small slope to this overturned car. Another comic lies in front of it.
Artifact #56: Power Plant Map
Just before entering the power plant proper, cut left to find a small security building. You'll find this pinned to the wall inside.
Training Manual #8: Smoke Chemistry
Just after Tommy points out the two engineers analysing the plant schematics, move just ahead to the desk with the oil lamp. Sitting on its corner is another manual.
Firefly Pendant #18
When you reach the room where the engineers are repairing the turbine, proceed to the ground level. Instead of going through the doorway where Tommy waits, head to the opposite side of the room to find a small storage space. In here, you'll find a cabinet with some hardhats... and another pendant!
Artifact #57: Plant Schematics
On your way outside during the bandit attack, stop by the same table where the engineers were perusing the plant schematics. You can now pick them up.
Tommy's Dam - Ranch House
Firefly Pendant #19
Once you've entered the ranch house, head to the back right of the bottom floor. In this sitting room, check the writing desk for another pendant.
Comic #8: Zero Point
Make a left at the top of the stairs to enter a bedroom. Take a left upon entering to find a comic near the window.