public int spawnPoints = 30;

     public GameObject spawnLocation;

     void Awake()
     {
         RaycastHit hit;

         for(int i=0;i<spawnPoints ;i++)
         {
             Vector3 position = new Vector3(Random.Range(-100.0f, 100.0f), 0, Random.Range(-100.0f, 100.0f));
             if (Physics.Raycast (position + Vector3 (0, 500.0f, 0), Vector3.down, out hit, 200.0f)) {
                 Instantiate (spawnLocation, hit.point, Quaternion.identity);
             } else {
                 Debug.Log ("there seems to be no ground at this position");
             }
         }
     }