GPS readings (all 18L)
1 0811106 8524506turnoff
2 0808005 8523984 crossroads
3 0807656 8524076junction
4 0804610 8521702bridge
5 0803933 8524626 office at Moray site
6 0804413 8524608 junction for bridlepath
7 0805128 8524356 
8 0805696 8524156 
9 0806236 8524122 
10 0806612 8524110 exit from ravine
11 0808400 8529516junction

Route:

We climbed the zigzags from Urubamba and took the signposted turning to Maras (1). This is a new surfaced road. After a couple of km is the junction with the dirt road for the salt pans. At Maras we crossed the plaza as shown, and turned right at a crossroads (2) where a direction sign is painted high on one of the walls. As you leave the town you come to a fork with a notice explaining that the righthand route is a bridlepath (camino de herradura) reaching Moray after 5 km and the lefthand route a vehicle road reaching the same destination in 9 km. We took the road. It makes a dogleg in order to cross the Q. Huayllaoro ravine high up.

There is an office of the Peruvian archeological organisation at the site (and lavatories). When we left we asked for directions to the bridlepath back to Maras, and it was pointed out to us. It forks left from the road at 6. At 7 you ignore a couple of paths connecting with it, one of which has a blue slab as a signpost on it.

At 8 and 9 we took photos of each other.

The ravine at 10 is a significant obstacle, not entirely rideable. As you emerge a path joins from your left. I think that this path leads somewhere different, so if you follow the bridleway in the opposite direction, aim to cross the ravine as high as you reasonably can.

Maras comes into sight soon after leaving the ravine.

For the salt pans, head back towards the Urubamba road and take the signposted dirt road to your left. This drops gently at first, and then gaily plummets, giving excellent views. At the saltpans it declines from road to footpath, and you will need to carry your bike some of the way down. You cross the Pichingoto bridge and join the main road.

We would not particularly recommend climbing from the Pichingoto bridge to Maras with a bicycle, but it has been done.