The previous poster made a huge mistake and took one of several roads in the area. A couple do connect with Mortirolo and this is what happened to him. The original post (mine) said it was obscure, hard to locate and not on the GPS. Ignore this and risk what Gavin went through.
Sorry Gavin, but what you wrote is totally wrong = there are NO ROCKS on Paso Mortirolo, not is there any dirt. Its a major Tour de France route with very good tarmac the entire way. The west climb has roughly 38 hairpins and never counted the number on the east ramp. Ive did this route on a Multistrada in 2006 and again on a 1098s superbike in 2010. It is a superb ride for any motorcycle! You don need a GS or supermoto.
Gavin says don do it. I say DO IT. If in doubt as to where it is, ask a local in Mazza or Monno. BTW, its easier to find in Monno, but better ridden from Mazza.
I made a big mistake with this route, so be warned so as not to repeat.
The problem is where the route starts, i.e. not on a major route.
When I got close I told my satnav (zumo) to joint this route that I had downloaded from here. What it has done I think is take me from that position to somewhere along the route using the shortest route and ignoring the beginning ( I made the wrong choice to define the start). Where it started me from was N46 14.513 E10 14.721
Unless your are riding solo on a GS or real trail bike, do not take this. It led up some beautiful single track roads with stunning scenery, but there were miles of really rocky passes. Im okay off-raod but was getting seriously concerned at times a> with what lay ahead and b> with the possibility of damaging a tyre and rim on the R1150RT with fully laden panniers, tent etc.
Anyway, all part of lifes rich tapestry!
Passo di Mortirolo isnt on many maps, let alone most GPS and most will not show the road correctly. Its a fantastic route connecting Mazzo and Monno villages, well paved, twisty, narrow and beautiful scenery. Im guessing it must be about 20 - 30 kms long and is just shy of 2000m altitude. It is little used and locally best known as a route on the Giro dItalia bicycle race. To find the pass - if riding from Switzerland over Bernina Pass to Tirano, take the highway towards Bormio and Mazzo is about 5-7 km. Watch carefully for the sign Passo di Mortirolo on the right. If riding from Bolzano (or south over Passo di Gavia) heading for Edolo, watch for the sign to Monno (about 5 km before Edolo) as the Passo itself is not signposted. Id heard about this Pass at the hotel in Le Presse and decided to find it as part of my route to Passo di Gavia, the Stelvio and beyond. I cant recommend these 3 highly enough, taken in either direction for a day ride adventure - you wont be disappointed. If you are quick enough and based in the area - you can easily go over the 3 and back again - Enjoy!