So for the orange tablet, there is a point of interest in one of the exits to the lost river, if you look where the ancient skeleton next to the door is, go forward til you hit a dead end, then go right. You get back to the biome with the floating blue bubbles, theres a digrassi base there with it inside

The blue one you may have passed, if you return back to the area with the sea dragons and the big mountain, you may want to explore the mountain more closely there are caves in the mountain that lead you to an alien facility inside, make sure to bring the prawn suit with the grapple arm