Borderlands 3 has 30 Eridian Writing Slab Locations. Finding all Eridian Writing Collectibles unlocks the Tales From The Eridian Slab trophy or achievement.

None of these collectibles are missable! You can still get all of them after the story in free roam. Some require you to have done specific side missions as will be pointed out in the guide.

When you get close to an Eridian Slab it will be marked on the map via a blue icon. However, you won't be able to read it until you unlock the ability near the end of the game (automatic from main story and unmissable). So beat the story first and collect them after.

The ones you found get a different icon on the map. You can also keep track by pressing L3 / Left Stick on the world map / in orbit / in zone map to view how many you found.

You also earn 25 Eridium per Slab, which is Borderland 3's premium currency to buy skins and customization items from the Crazy Earl merchant in Sanctuary. 30 Slabs x 25 Eridium makes 750 Eridium earned in total.

It is best to do this after the story. The story will bring you to all of these areas automatically. During the story some areas are not yet accessible but you wouldn't be able to decipher the slabs anyway.

Trophy Bug Warning: The trophy often glitches and doesn't unlock after the 30th writing. You can fix this by scanning the story-related Slab in Sanctuary, in Tannis's infirmary again. Scan it a few times and the trophy should unlock. The tracking for it in orbit view is also known to be broken and shows 34/30 or 36/30 Eridian Slabs found even though there are only 30 total.