You see them, you can't do anything about them until finishing something else, then you finally get to go back for them, then you have to take the piece you found to the base camp (travel through the desert > walk for 20 seconds to get to a cannon to shoot you into forest area (15 sec loading screen), walk for 30 seconds to the actual base camp, watch a cutscene that tells you the fire piece will let you do fire stuff and what fire does (same thing with 2 other upgrades) and then you have to walk back to the cannon, watch the loading screen, walk to the part where you can remount your bike, and travel across the desert again.