The forests of the Escarpment reflect their history, location and topography. The retreat of the glaciers, particularly on the ridgetops and northern and eastern slopes, scoured the rock, further distressing the growing environment on what are the Catskills' steepest and most exposed slopes. As a result, the coniferous evergreen species characteristic of boreal forests such as red spruce and the balsam fir Bartram sought appear in much higher concentrations, and at lower elevations, then they do elsewhere in the Catskills. The summit of North Mountain, at 3,180 feet (970 m) above sea level, is covered in boreal forest, the lowest Catskill summit of which this is true. While there are no true alpine zones in the Catskills, Kudish has found the only areas in the range which come close along the Escarpment at elevations between along the Escarpment as it rises from lakes to North Mountain. These are exposed ridgetops where three-toothed cinquefoil, and in one mountain sandwort, is found. Since those species are shade-intolerant, it suggests that the sites have not reforested since the end of glaciation.