>>48053575OP here, I think I figured it out. I decided to try out the strategy I mentioned where you use the sledgehammer on boulders and dark spots, then use the pickaxe to crack light spots to check for anything underneath. Pic related, 3 items are visible. I was only able to dig up a yellow shard, a large red sphere and a small blue sphere before the wall collapsed. There were apparently more items but I couldn't find them. In the OP image I wasn't using this strategy, I was just digging randomly. I think if I use the strategy in pic related I can find items easier.
