As soon as I was able to leave the Sacred Grounds, I stopped doing the main quest and began exploring.
When I attempted to go to the second Tallneck, however, I ran into the Daytower and I was told that the gates would remain sealed until all corrupted zones in the valley had been cleared. After that, I went and cleared every corrupted zone I could find and explored every part of the map that I could, until there didn't seem to be any more corrupted zones.
However, the Carja guards still refuse to let me pass, despite having cleared all corrupted zones on the accessible area of the map. How do I get through the gates?