Matawatchan Provincial Nature Reserve, on the southern portion of the Canadian Shield, features ancient sedimentary rocks that have been changed, or metamorphosed, by pressures from deep within the Earth's crust. These Precambrian rocks include biotite gneiss, quartzite, marble and granite. The nature reserve lies in a forest region noted for its deciduous-evergreen transition. The reserve is dominated by forests of sugar maple, hemlock, yellow birch and beech. A small valley within the reserve supports large American elm and red maple, and red spruce which approaches its western range limit here. Lowland forests include white cedar and balsam fir, meadows, marshes and thickets. The marble outcrops in the reserve are of special botanical interest as they support walking fern as well as several other calcium-loving plants. There are no visitor facilities. The unauthorized collection of rocks, plants or other natural objects is prohibited. Anyone wishing to conduct research here must obtain an approved research application.