SwapStone Circle is an area set in a large open field, separated by one continuous snake-like hummock that serves as a footpath between two of its three Totem Poles. Upon interacting with the lowest Totem Pole in this area, Krystal can start a timed mini-game where she's encouraged to sprint along the grassy hummock and leap across a newly raised platform to reach the sister Totem Pole in under 45 seconds.
Unfortunately, this puzzle appears to be incomplete, and will not acknowledge her arrival to the second Totem Pole.  

Krystal can find the eponymous SwapStone, Rubble, in the center of the Circle, which serves as the prime motivation for visiting this area at any time during her adventure.

From SwapStone Circle, Krystal can discover a branching path to Lightfoot Village/Cape Claw, a secret underwater passage to Discovery Falls and the gate that leads to Golden Plains. 

When Krystal is reunited with Kyte, she can return to SwapStone Circle and light the torches around the area to meet with Chief Lightfoot, who soon becomes a familiar face in the Circle. 

Unlike its counterpart in SwapStone Hollow, the Circle doesn't appear to facilitate any class of dinosaur within its domain, with the nearest LightFoot Tribe contained within the walls of their own Village. 

NPC's: 

Rubble: Allows Krystal to swap to Sabre's Adventure, and travel to Warlock Mountain/Cave of Treasures.

Chief Lightfoot: Appears in the Circle to showcase a route to Discovery Falls, and impart Krystal with quest items.

Key Items:

Shiney Nugget: The first Nugget can be found near the Golden Plains - cannot be used on the BribeClaw.

Moon Mountain Pass Key: Given to Krystal in SwapStone Circle by the Chief Lightfoot.

SharpClaw: Found nearest the entrance to Cape Claw.

Moon Mountain Pass Key Bug: Chief Lightfoot may not appear to give Key, despite having met all requirements. 
Status: Manageable.
Solution: Restarting the game and resuming Krystal's Adventure, or adding the Key to inventory using a code.
 

SwapStone Circle is one of the most stable areas in Dinosaur Planet, and despite the Totem Pole puzzle being incomplete, does not pose any outward problems towards completion of the game. 

While SwapStone Hollow would appear in Starfox Adventures as ThornTail Hollow, SwapStone Circle was made redundant by Krystal's removal, and cannot be found in the GameCube adventure in any capacity.