Access: This trek starts at Laguna San Marcos, which can be accessed by vehicle from Cayambe via Olmedo. Cayambe is 27 kilometers (17 miles) south of Otavalo and 53 kilometers (33 miles) north of Quito. There is frequent bus service to Cayambe, but not all buses from Quito to Otavalo or vice versa take this route, so ask the driver. Quito to Cayambe takes 2 hours, $1.50; Otavalo to Cayambe 40 minutes, $0.60. From the corner of Restauración and Vivar in Cayambe, take a bus to Olmedo, 18 kilometers (11 miles); frequent service, 45 minutes, $0.40. A dirt road runs east from Olmedo to Laguna San Marcos. Pick-up trucks can be hired in Olmedo for the trip; 40 minutes, $10. Pick-ups direct from Cayambe (Junín corner Azcázubi) to Laguna San Marcos charge about $25.

Route: Start at the ranger station at the south end of Laguna San Marcos. From here follow the unpaved road north. In 5 minutes you reach a fork; turn left onto the road which goes west toward the lake and follow it to the end, reached in 25 minutes. This section can also be done in a four-wheel-drive vehicle, ask your driver if he can take you all the way. There is a camp site at the trailhead, sadly strewn with trash.

Cross the small inflow of the lake and continue north, following the western shore of Laguna San Marcos along a trail used by fishermen. The forest is very nice and there are lovely views over the water, but the going is difficult with a pack, not only because it can be muddy, but also because of the many tree trunks you have to crawl over or under. Some of these trees, among them quishuares and pumamaquis, have a diameter of 50 centimeters (20 inches)-large for this elevation-suggesting they are quite old. The vegetation is thick with mosses, and epiphytes cover the trees. There are several clear streams along the way. In 1.5 hours you reach a pretty spot suitable for camping by the lake shore.

Continuing north along the trail for another 2 hours, you emerge from the forest to open grassland with low bushes and a great deal of sword-grass (wear gloves to protect your hands). You are now at the north end of the lake, by Quebrada Quilpajahua, one of its inflows. The views south over Laguna San Marcos to Cayambe are magnificent, and will accompany you for the next day or two. Climb gently north following an increasingly faint and narrow trail along the west shore of Quebrada Quilpajahua. In a few places, high banks will force you to climb above the river, but you then return closer to the shore. In 1 hour you will reach several flat spots suitable for camping along the river, where the trail fades away. If you have a fishing rod, you might catch your dinner here. Take water and get an early start for the climb ahead.

Climb northwest cross country, moving steadily away from Quebrada Quilpajahua. Pick your route through the scrubby vegetation, avoiding the few patches of larger trees. As you climb, the sword-grass and bushes gradually yield to straw, making the going easier. In 2 hours you reach a wide balcony above Quebrada Quilpajahua and you can see the ridge stretching between Cerro Jatuncunga and Loma Camasigana, above you to the northwest. Continue northwest, at first level along the balcony and then climbing steeply through the now open country toward the crest of the ridge.

Aim to reach the ridge top just above the source of an unnamed tributary of Quebrada Quilpajahua, which flows in from the west. As you attain the ridge top (2 hours from the balcony), you will see Cerro Jatuncunga (3,879 meters, 12,727 feet)-a great mass of rounded stone-nearby to the west, and below it further west, the broad valley of Quebrada Chaguancorral. Behind you, to the south, Cayambe still looms magnificent above Laguna San Marcos. Northward, along our route, is the rocky outcrop of Loma Camasigana (3950 meters, 12,960 feet, labeled Cerro San Francisco on the 1:25,000 scale topo map). Note the chewed-up achupalla leaves, a sure sign that Spectacled Bear visit this area.

At this point you have the option of continuing the trek north to Laguna Puruhanta or making a shorter loop by returning to the Olmedo-Laguna San Marcos road via the Filo de Ismuquiru ridge. The authors have not taken the latter route. Note that from where you reach the road, it is 11 kilometers (7 miles) back to Olmedo, and there is little or no traffic.

To continue on to Puruhanta (the more difficult part of the trek), go northeast for 30 minutes, along the ridge line that climbs steadily from Cerro Jatungunga toward Loma Camasigana, taking in the splendid 360 degree views. In poor weather, contour east of the summit of Loma Camasigana and head toward an unnamed saddle, 30 minutes ahead, between Loma Camasigana and Cerro Yanajaca (3903 meters, 12,806 feet). In good weather, it is worth detouring north for 1 hour to the rounded summit of Loma Camasigana, for more spectacular views in all directions.

North of this summit, the ridge line becomes very narrow and craggy. Our route therefore turns east, following an east-west ridge for 20 minutes, down to the saddle mentioned above. This is the watershed between Laguna San Marcos, to the south, and Laguna Puruhanta, to the north. The views of both lakes are wonderful, and Laguna Puruhanta seems "just up ahead"-a most deceptive illusion. What seems like the direct route, straight down to Laguna Puruhanta, is not feasible because of bogs, dense vegetation, and cliffs. It can be quite windy at the saddle. Continue east beyond it and then descend north to a flat straw-covered area, suitable for camping, 10 minutes ahead. There is water in small ravines below.

From the saddle mentioned above, a faint trail makes a wide circle as it descends, traveling at first east, then northeast, and later northwest. It drops gradually from one terrace to another, through soggy páramo. Twenty minutes from the camping spot you will reach a narrow wooded ridge to the west of which is a stream. Follow the ridge, then drop steeply northeast to emerge at a swampy plain in 10 minutes. Head northwest over the plain to reach, in 15 minutes, the base of a high ridge which lies to the west. There are some soggy spots to camp in this area. Take as much water as you can here and once again get an early start for the long climb ahead.

Continue north along the base of the high ridge, in 5 minutes you will reach a trail that climbs steeply west, and a much fainter trail that drops north and soon disappears in thick vegetation. Follow the trail west up to the ridge top in 1 hour. Take the ridge line north; it undulates considerably making for difficult going, but the superb views of Laguna Puruhanta to the northeast, surrounded by an endless array of craggy peaks, makes the effort worthwhile. In 1 hour you reach a jagged rocky outcrop on the ridge which must be circumvented to the east. Drop slightly and contour to regain the ridge line at a broad saddle 30 minutes beyond. There are no proper camping spots along the ridge, however the only place barely suitable for a tent is below the base of the outcrop mentioned above. There may be a trickle of water running over the rocks here after rain.

The next summit north along the ridge is Cerro Negro Rumi. It is a 30 minute climb to the rounded, straw-covered summit, labeled Cerro Negro Rumi on the 1:25,000 scale map but labeled only point 3945 meters (12,944 feet) on the 1:50,000 (which shows Cerro Negro Rumi further west). The summit offers outstanding views over Laguna Puruhanta and the surrounding mountains-another worthwhile detour in clear weather.

The descent to the lake is the most difficult part of this trek, as it is hard to push through and navigate in the dense scrub forest. The trail to the lake indicated on the IGM maps no longer exists. On your way down, look ahead for grassy areas where you can advance faster. Patches of forest have been burnt, and it is much easier to move along them.

From the summit of Cerro Negro Rumi, backtrack southeast for 10 minutes to a pair of bare black crags. Cross through a notch between the crags, then contour south at the base of high cliffs. In 10 minutes you will reach a gully which drops steeply to the southeast. Descend along the gully through increasingly dense straw, sword grass, and small bushes, alongside a few low rocky outcrops on both sides. In 1 hour you will reach a point where the vegetation turns to forest. The gradient here is less steep than in other parts of the descent; you can pitch a tent if you have to, although it is by no means flat. There is a small stream on the north side of the gully for water.

The going from here becomes especially slow and difficult. The scrub forest is very dense, and you must clear the path ahead of you. Since the vegetation is somewhat thinner along the ridge lines than in the valleys, try to continue along the ridge top south of the gully. There are some vague animal trails on this ridge. Follow them east and northeast, staying on the ridge top whenever possible. In 1 hour you will reach the end of this forested ridge, at the intersection of two drainages. Cross the stream to the north and climb to another low ridge top along which you continue to descend east. In 10 minutes you reach the first of several patches of grassy slope (old burnt forest), separated by small tatters of woods. Maintain a northeast course downhill, taking maximum advantage of the clear areas to loose elevation. In 30 minutes, the open slope gives way to mature forest, with tall trees and relatively sparse undergrowth. Continue to descend east through the forest, it is still steep, but easier going than in the scrub higher up. In 45 minutes you will finally emerge onto grasslands by the lake shore. Puruhanta is a very beautiful lake, nestled amid impressive forested mountains with great craggy peaks.

There is a muddy fishermen's trail along the western shore of the lake and several campsites along the way (with fishermen's trash). A particularly nice, large camping spot is by one of the inflows, a worthwhile 30 minute detour south from where you reach the shore. The trail continues to the south end of the lake, a good area to observe water birds.

From the large campsite mentioned above, return north along the muddy lakeshore trail through open grassland and bog, with the cliffs of Cerro Negro Rumi towering above you to the west. In 45 minutes, the trail ducks into the woods and climbs high above the lake in order to skirt precipices by the water's edge. The trail is well-used but nonetheless difficult because of deep mud, tangled masses of fallen trees, and large trunks under which you must crawl. In 3.5 hours you reach an unnamed stream where it enters the lake; there are several campsites nearby.

If you continue north along the trail, you will reach the source of the Río Pisque, the lake's outflow, in 45 minutes. If the level of the lake is low, however, you can walk north along the shore, in ankle deep water (much easier than the trail) to reach the Río Pisque in only 15 minutes. At the source of the Río Pisque are several trashed campsites, an abandoned hydrographic station, and a tarabita (primitive cable car) crossing the river. The views southeast over the lake to Loma Potrerillos (3902 meters, 12,803 feet) are superb.

Cross the Río Pisque at its source, either by wading through the lake just where the river starts or, if the water is too high, by using the tarabita. A good but muddy trail descends northwest along the eastern shore of the Río Pisque, through pretty cloud forest. In 1.5 hours you will reach a large open swamp where the trail deteriorates to a soft, muddy swath. Follow the swath northwest to cross the swamp. In 15 minutes you reach a dry patch by a small stream, suitable for camping. This spot is known as Potrerillo. From here you can see the houses and pastures of Nueva América: your destination perched on a steep hillside to the northwest.

Continue northwest, still walking through bog, now amid reeds. In 15 minutes you re-enter forest and a further 15 minutes ahead you reach a pretty unnamed stream, with a very small area suitable for camping. From here the trail becomes narrower and, in parts, goes precariously high along ledges above the Río Pisque. At one point, you even cross under a small waterfall!

One hour after the stream mentioned above, you reach a large trunk cast across the Río Pisque, where you cross the river to the west bank. If the water is low, you can ford the river below the trunk, otherwise you must walk over it. From the crossing, the trail climbs steadily northwest. In 30 minutes you will reach a pasture with more fine views ahead to Nueva América, from where the trail drops steeply to the Río Molinoyacu (locally known as Río El Tornillo or Río El Molinillo), reached in another 30 minutes. At low water you can ford the river, otherwise look for a log bridge.

The trail climbs on the north shore of the Río Molinoyacu. Just a few minutes ahead, a smaller trail branches off to the right and descends to another log bridge across the Río Pisque. The trail on the east shore of the Río Pisque leads to the village of Shanshipamba, an alternate way out (with road connections to Pimampiro). The authors have not taken this trail. Our route follows the main trail climbing north above the west shore of the Río Pisque. You will reach a small pasture suitable for camping 10 minutes after crossing the Río Molinoyacu. Another 15 minutes ahead you will reach a larger pasture with a private house; beware of cattle in this area. Descend north for 15 minutes through the pasture, toward the confluence of the Río Pisque and the Río Palaucu; there is a small patch of woods before you reach the river.

Ford the Río Palaucu above its confluence with the Río Pisque to reach another large pasture on the north shore. Climb northwest through this steep pasture, along a barbed-wire fence. In 15 minutes you will reach a clear horse-packing trail which climbs steeply to Nueva América. The trail zigzags amid cliffs, providing great views up and down the Río Pisque Valley. Bird songs accompany you along the gradual 2 hour climb to Nueva América, a tiny hamlet, home to only five families in 2002. If you are lucky, clear skies will afford a view all the way back to the glaciers of Cayambe-a grand finale to this tough and rewarding trek.

Getting back: From Nueva América it is a 2.5 hours walk north along a vehicle road to the small town of Mariano Acosta. Along the way, from the area marked La Florida on the IGM map, you can see Mariano Acosta to the northwest and take a shortcut which avoids a long detour along the road. From Mariano Acosta there are regular buses and pick-ups to Pimampiro; the last one leaves at 1700, $0.50, 1.5 hours. From Pimampiro there are buses to Ibarra every 20 minutes, 1.5 hours, $0.80. Ibarra, capital of the province of Imbabura, is 20 kilometers (12 miles) north of Otavalo and there is frequent transport between the two.