San Rafael is a medium-sized city (some 50,000 inhabitants), is an important vineyard and winery area, but also has beautiful places that, in some cases, can be visited by bus. Valle Grande,the lower part of the Atuel Canyon, is only 20 miles away and can be reached in the local bus services, Empresa Buitroni. If not, a taxi there will cost you $20-$25, or you can take a local tour, that will require 8 hours less than if you take a tour from Mendoza city. Valle Grande is a relatively easy rafting area and, downstream from the dam, there is class II rafting with some rapids, but only problematic for kayaks; I saw one upside down. It is near to the upper Atuel Canyon, but if you are not fond of exhausting trekking, you might as well go on an organized tour. Of course, you can stay at the three-star Valle Grande Hotel and Resort and leave early in the morning.
It is said to be a rainbow trout fishing area; that is probable, although the only time I tried to fish in the canyon I had no luck. Upstream from the Nihuil Lake, on the bridge of Highway 40 at El Sosneado, I have fished many five-pound trout, but as there is no dam upstream on the river, water generally is not clear, and you need clear water and no wind to have a good chance. That happens usually at the beginning of the fishing season, in October, before snow starts to melt rapidly. If you go to El Sosneado, you will see the snow-covered Andes at a distance. Of course there is nowhere to stay at El Sosneado, so you would need to go to the nearest town, Malargue, that is some 30 miles south of El Sosneado, and at a slightly larger distance from Las Leñas, the most important ski centre in Mendoza, or take the bus from San Rafael to El Sosneado; it only takes 2 hours and 10 minutes, and leaves at 9am.
Valle Grande seems like the Far West scenes we are accustomed to in cowboy movies. It does not have any vegetation, except by the riverside. The Valle Grande Dam is 150 feet high, and if you walk up to the top of the dam you will see the Submarine, a natural formation that disappears under the water when the dam is full. About three to five miles up the road, you will already be in the canyon. There are four power plants in the canyon, where the water of the river disappears to return further downstream. The water is crystal-clear, is always running, and there are beautiful pools in the river where you should be able to fish beautiful trout. I did not succeed in the attempt.
Upstream from the canyon is the Nihuil dam and lake, probably the most important hydroelectric project in Mendoza. The lake is large, and trolling is said to give very nice results, with trout weighing up to eight pounds. You might want to give it a try.
El Nihuil has a small tourist village with some infrastructure, located 40 miles to the southwest of San Rafael. There are local buses to El Nihuil, and you can also walk from there down the river to admire the canyon. That is what I did in 1970, when I walked maybe ten miles down the canyon. The view is very attractive.
Of course, the Nihuil Canyon is a fraction of the Grand Canyon in the USA and even a smaller fraction of Copper Canyon in Mexico. It is probably a thousand feet deep, at the very most, but it is still an enjoyable scene, that runs along a geological fault.
Nearer to San Rafael there are a number of dams, of which I remember the Galileo Vitale dam, near the city, where you can probably fish nice rainbow trout in the lake, or downstream from the dam, and San Rafael is only three hours by bus away from Las Leñas.
To the north of San Rafael, about half way between San Rafael and Mendoza, you can visit El Manzano Histórico, where you can fish two-pound rainbow trout in the Arroyo Grande. Fish near the campground, because if you go too far upstream you will fish many trout, but very few will weigh more than half a pound.
In the area of El Manzano Histórico you have the relatively nearby cities or villages of Tunuyan, Tupungato, and Campo los Andes, that have regular bus services to Mendoza, that run about every hour. I would definitely visit the area south of San Rafael, especially the Atuel Canyon, the rafting area on the Atuel River, El Sosneado for trout fishing, or trolling in the Nihuil lake, and Las Leñas.
Rafting is not expensive at Valle Grande, it should be costing around $5-$6 per hour.
South of Malargue you have another good fishing area, Bardas Blancas on the Río Grande, where many years ago they fished an 18-pound rainbow trout. But the place became famous and was over-fished. I always got better results fishing in the Atuel River at El Sosneado. If you go to Las Leñas, you can try fishing in the Valle Hermoso area, also on the Grande river, since it is less visited by fishermen.
The bus companies that cover this area are TAC though it's not my choice, and Andesmar (www.andesmar.com.ar). Andesmar buses from Mendoza to San Rafael run six times in the day. There you will have to connect to local bus services, probably TAC. There is one bus in the day of Andesmar from San Rafael to El Sosneado that leaves at 9am.
This tour covers a total distance of 606 kilometers (370 miles) and is rather tiring, so sleep well the previous night, or travel to San Rafael, stay overnight, and take a local tour from there. You will travel some 80 miles instead of 370.
Enjoy your stay in Mendoza. I am sure you will.