Strange Edge Shadow on Generated Plane Mesh

I'm trying to generate a flat mesh which will later become terrain, although I successfully generated the mesh, it generates with these weird shadows on two of the edges (opposite each other). i initially though it was an issue with the Texture I was passing to the mesh material, but the problem still occurs with no texture applied which leads me to believe there's something wrong with my vertex/triangle generation. I was hoping someone who is a little experienced with this stuff could shed some light (no pun intended) on this issue.

I'm also including the mesh generation code I'm currently running but I'm not sure if that's really the issue since I've done the mesh generation two different ways with the same shadow issue.