Get out of my (Mountain) Face!

Thesis takes a long look at the route ahead. ‘Why a river? Why a mountain?’ he thinks. ‘Give me a Giant or a Dragon instead!’.
Still leading his horse through the icey waters, Thesis trudges onwards in his oddly quiet but heavy, magical full plate armour. It had cost him a small fortune and it had halved his formally impressive speed, but the added protection it had given him more then made up for it.
Struggling out of the water, Thesis notices the strange rock formation. It seems to be an upward jutting lip. Looking up the path he can see it’s only about 300 feet to the top but very steep; Maybe one feet up for every one foot along. The path lies between two seperate peaks and at the edge of the path is an almost sheer rise either side. Weirdly, at the top are several piles of boulders. Aside from these features, the mountain is devoid of any vegetation or signs of animal life.
Dragging his unwilling horse behind him, Thesis heaves himself upwards.
The ground begins to shake and when he’s just 30 feet up the path, the first set of boulders, unbidden, start to roll down the slope. They gather speed as they go and despite his best efforts several crash into him. His magical armour does little to protect him and although he keeps his footing, he’s hurt.
Thesis has only two choices: Run back down the 30 feet or slog up the remaining 270 feet. As usual, Thesis chooses the confrontational option.