Observation point: from Alpisella pass or from mountain hut that overlooks the view 
 
This is the Alpisella pass: it connects Bormio to Livigno through Fraèle valley, once a frequented highland for grazing cattle and iron mining. 
From this point to the west, the quite flat green surface is suddenly cut by the deep incision of the creek running down towards the artificial lake of Livigno; to the East, on the contrary, a wide, gentle sloping valley develops for about two kilometers, before turning into a narrow gorge opening into the artificial lake of San Giacomo. Both of them are named Alpisella valley, perhaps because of the omogeneous flat area at their boundary, without an easily perceived separation point.  
The stright east-west trend of the Alpisella valleys is controlled by the geological structure of the area: along this line, infact, during alpine orogenesis the massive, dolomitic mountain ridge at the northern flank overthrusted the younger stratified marlyl limestones and marls of the southern flanks; near to the thrust plane, dolomites were pervasively fractured and became brittle, so erosion could easily mould the two valleys.  From here, you can still see the remnants of tectonized rock on the crests, and the continuous debris sheets originated by their disintegration. 
Despite its smooth appearence, together with Val Trela and Foscagno passes, Alpisella is one of the most interesting saddles of high Valtellina. 
From this point, in fact, rain water falling eastward of this saddle, infact join Adda, whose sources are a bit lower from the vantage point, tributary of river Po, which in turn goes into the Mediterranean sea, while waters falling westward feed river Spol, going into the Inn, then from it into the Danube, and finally in the Black Sea. 
In one word, this is the watershed between mediterranean and Black sea basins, a very important european boundary!