Ember Valley is one of the main starter locations in Slime Rancher 2. It's a hot area that offers a lot of resources and slimes for you to find and return to your base. This location is locked by progression rather than story. You will need to do a direct thing to unlock this area in Slime Rancher 2.
How to find Ember Valley in Slime Rancher 2
After discovering a particular slime, the Pink gordo, it will be available in Slime Rancher 2. It's a massive slime that has been lumped together with several other pink slimes and cannot be moved. The only way to get rid of it is by consuming it a lot.
The Pink gordo you see at that location will accept almost anything, and it will eventually become sick and explode into many Pink slimes. Under the Pink gordo, there will be a device to interact with, and it will lower a wall and show you a platform to stand on.
When you reach the platform, you can now go to Ember Valley. You can find many slimes here, which is an excellent location to find Radiant Ore.