Commencing in the middle of the channel of the Deschutes River opposite the eastern termination of a range of high lands usually known as the Mutton Mountains; thence westerly to the summit of said range, along the divide to its connection with the Cascade Mountains; thence to the summit of said mountains; thence southerly to Mount Jefferson; thence down the main branch of Deschutes River; heading in this peak, to its junction with Deschutes River; and thence down the middle of the channel of said river to the place of beginning.