“ Provided, however, That any tract or tracts to which valid existing rights have attached under the laws of the United States providing for the disposition of the public domain are hereby excepted and excluded from the reservation hereby created: And provided further, That if at any time the lands covered by any valid claim shall be relinquished to the United States or the claim lapse, or the entry be canceled for any cause whatever, such lands shall be added to and become a part of the reservation for the Pueblo of Santa Clara, as herein provided for. ”