IndexOutOfRange Issue

When I enter play mode, I keep getting the following error in the console:

IndexOutOfRangeException: Index was outside the bounds of the array. Grids2D.Sprites.PlaceSprites () (at Assets/Sprites.cs:90) Grids2D.Sprites.Start () (at Assets/Sprites.cs:57)

Here's the code:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using Grids2D;
 using System;
 using Random = UnityEngine.Random;
 
 namespace Grids2D {
     public class Sprites : MonoBehaviour
     {
         public GameObject redBall;
         public Grid2D grid;
         private float[] xSpriteCoords;
         private float[] ySpriteCoords;
         private int numberOfSprites = 5000;
 
         TERRAIN[] terrainAssignments;
         public enum TERRAIN
         {
             Open = 0,
             LightWater = 1,
             LightWater_Road = 2,
             HeavyWater = 3,
             HeavyWater_Road = 4,
             LightWood = 5,
             LightWood_Road = 6,
             HeavyWood = 7,
             HeavyWood_Road = 8,
             Village = 9,
             Road = 10,
             LightHill = 11,
             LightHill_Road = 12,
             HeavyHill = 13,
             HeavyHill_Road = 14,
             Impassable = 15,
             HeavyWater_HeavyHill = 16,
             HeavyHill_Village = 17,
             HeavyWater_Village = 18,
             LightHill_LightWood = 19,
             HeavyHill_HeavyWood = 20,
             HeavyWater_HeavyWood = 21,
             Road_Impassable = 22,
             Impassable_Impassable = 23,
             HeavyWater_Impassable = 24,
             LightWood_HeavyWood = 25
         }
 
         void Start()
         {
             Debug.Log("started");
             xSpriteCoords = RandomPointCoords();
             ySpriteCoords = RandomPointCoords();
             Debug.Log("randomized coordinate arrays");
             //Instantiate(redBall, new Vector3(xSpriteCoords[5], ySpriteCoords[5]), Quaternion.identity);
             terrainAssignments = TerrainAssignments(); //assign the values of the terrains array with AssignTerrain
             Debug.Log("generated terrain assignments");
             PlaceSprites();
             Debug.Log("placed sprites");
             Debug.Log("ended");
         }
 
         private float[] RandomPointCoords()
         {
             float[] array = new float[numberOfSprites];
             for (int i = 0; i < numberOfSprites; i++)
             {
                 array[i] = UnityEngine.Random.Range(-250f, 250f);
             }
             return array;
         }
 
         private TERRAIN[] TerrainAssignments() { //returns an array of terrain assignments corresponding to ammount of cells
             TERRAIN[] array = new TERRAIN[grid.numCells];
             Debug.Log(array.Length);
             for (int i = 0; i < grid.numCells; i++)
             {
                 array[i] = (TERRAIN)Random.Range(0, 25); //sets terrain type to something completely random
             }
             return array;
         }
 
         private void PlaceSprites()
         {
             TERRAIN terrain;
             for (int i = 0; i < numberOfSprites; i++)
             {
                 Debug.Log(i);
                 Debug.Log("terrainAssignments.Length = " + terrainAssignments.Length);
                 Debug.Log("xSpriteCoords.Length = " + xSpriteCoords.Length);
                 terrain = terrainAssignments[grid.CellGetIndex(grid.CellGetAtPosition(new Vector3(xSpriteCoords[i], ySpriteCoords[i])))]; //gets what terrain is at the random coordinate
                 if ((terrain == TERRAIN.HeavyWood) | (terrain == TERRAIN.HeavyWood_Road) | (terrain == TERRAIN.LightWood_HeavyWood)) //if it is heavy wood
                 {
                     Instantiate(redBall, new Vector3(xSpriteCoords[i], ySpriteCoords[i]), Quaternion.identity);
                     //Debug.Log("instantiated sprite");
                 }
             }
         }
 
     }
 }
 

According to my math, no index should be outside the bounds of the array at terrainAssignments array. Could someone help point out what I'm missing? If it helps, numCells is 30.

Thank you for your time.