The Mackenzie Panels are the remains of the former Clifton Gate Pioneer Memorial Arch, originally located in Niagara Falls. Unveiled in 1938, the arch was dismantled in 1968 to make way for a road widening. The arch had been built to honour the early pioneers who laboured to settle the land, and also to the memory of the martyrs of the Rebellions of 1837.

The panels were designed by C.W. Jefferys and sculpted by Emanuel Hahn. One of the panels shows Mackenzie presenting his historic Seventh Report of Grievances to the House of Assembly of Upper Canada. Names of those executed during the repression that followed defeat of the rebellion appear on one of the panels, as do profiles of the two rebels who met their death on the scaffold in Toronto, Samuel Lount and Peter Matthews.

In 1974, it was revealed publicly that the historic panels were stored in a yard of the City of Toronto parks department, prompting Toronto City Council to pursue the restoration of the panels. They were repaired in the workshops of one of the original carver-sculptors and found their place in the garden of Mackenzie House.