Hart Side (the hill side frequented by harts) is a subsidiary top on one of the east ridges of Stybarrow Dodd, which is a mountain (or fell) in the English Lake District, west of Ullswater on the main Helvellyn ridge in the Eastern Fells.

Some guide-book writers have treated Hart Side as a distinct fell, and have devoted a separate chapter to it.

A north-east shoulder of this swelling ends with steeper gradients on all sides and a scattering of broken crags ahead.

This is Glencoyne Head, where a corrie glacier formed during the final phase of the last ice age and created these steep cliffs.

The trench was probably dug by prospectors looking for an extension to the vein being mined beneath Green Side, and the hollow may have been the site of some shelter.

[2] A vigorous programme of exploration, both underground and on the surface, was begun in 1947 when it was clear that the Greenside Mine could not last much longer, but nothing was found.

[8] In Alfred Wainwright's 1955 drawing the trench looks much cleaner and fresher than it is today[1] The view from the summit is restricted both by the higher ridge to the west, and by intervening land to the east which conceals most of Ullswater.

From Dockray, or the two car parks on the A5091 road (which serve Aira Force), ascents can be made via Watermillock Common (or the slopes to the south of it) and Birkett Fell.

These rocks are part of a thick succession of lava sheets found around the western and northern sides of the Lake District.

The main entrance was in Glenridding at Lucy's Tongue,[8] but an exploratory level was driven into the cliffs at the top of Glencoyne, from just below the Miners' Balcony Path.

Topography: This part of the ridge runs roughly north-east for about 1+3⁄4 miles (2.8 km) from the Brown Hills at the foot of Hart Side.

Aira Beck has cut a steep gorge between Watermillock Common and Gowbarrow Fell, which continues the line of high ground further east.

[6] Summits and views: The highest point on Watermillock Common is Swineside Knott 1,814 feet (553 m), a rounded grassy mound but with some rocks protruding, especially on its steep eastern side.

Ascents: Apart from the lower slopes beside Aira Beck, around Dockray and alongside Ullswater, Watermillock Common is Open Access land.

One writer has claimed the ridge top near Common Fell "can be more of a wade than a walk",[2] but this was not found to be so early in 2014 after an unusually wet winter.

Geology: The oldest rocks found on the Watermillock Common ridge occur on the lower south eastern slopes (above Ullswater) where faulting has brought to the present surface an inlier of mudstone from the Tarn Moor Formation, the latest part of the Skiddaw Group.

Here and there the map shows beds of volcaniclastic sandstone or breccia, sedimentary deposits formed from the erosion of the volcanic rocks.

[10] Around the summit of Common Fell it shows areas of hyaloclastite, a rock made up of shattered angular fragments and formed by the quenching of lava in water.