This route is also called 'ruta de los pies', as described on a sign at La Joya (I added a photo). From the Grupo de los Cien hut I would recommend going the left side of the rock outcrop (photo added). I went up to the right the first day to acclimatize and it took me a lot longer. I suppose the cross mentioned in this route description and depicted in the photo in the heading of the route description is the 'Cruz de Guadelajara', also called 'Cruz de las Once'. I found it flat on its back (photo added). You see another big cross from the hut, one by the Club Alpino Mexicano(photo added), but if you are going left of the rock outcrop you won't pass it so don't go for it. Both way leads to the Cruz de Guadelajara. At the summit there was only one cross(photo added). I walked back to Paso de Cortéz from La Joya, which took me two hours and hitchhiked to Amecameca from there.