Mason retired from architectural practice when he became Mayor and subsequently devoted himself to an estate in north Otago, the Punchbowl at Maheno. The partnership with Clayton ended in 1868 and in 1871 Mason formed a new one with his old clerk of works, Nathaniel Wales (1832–1903). Wales himself became Dunedin's mayor during the 1890s. Now in his seventh decade, Mason remained a vigorous designer. He completed Bishopscourt in Highgate for the Anglican bishop S.T. Nevill in 1872, and St Matthew's Anglican church in Stafford Street was started in 1873. The large stone house, high on the ridge behind the city, is somewhere between the perpendicular and Tudor forms of Gothic. It was later extended and survives as the core of Columba College, a Presbyterian girls school.