Here is the full list of all 30 Valley achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Complete game without the valley dying
Complete the Astra Facility
Stop the Astra Facility from killing the valley
Defeat the Alpha
Complete Smoke Lake
Take 10,000 steps
Defeat 25 dark creatures
Complete the Proving Grounds
Collect 100 acorns
Complete Camp Henday
Spend 20 minutes of accumulated time in mid-air
Find Virginia's music box
Complete the Soma Reactor
Acquire the Lifeseed
Complete the Soma Facility
Pacify 10 amrita swarms
Complete Titan Rock
Revive 100 trees
Complete Susurrus Valley
Complete Wendigo Lake
Drop down the pit located in Proving Grounds
Collect enough medallions to access all pyramid chambers
Kill 50 trees
Take life from 20 animals
Acquire all upgrades for the L.E.A.F. suit
Gain entry to the Sussurian Pyramid
Gain entry through all the acorn doors
Collect all energy upgrades
Discover the secret Landshark encampment
Find all 8 pages