I stopped in Malargüe on my way to Mendoza on Route 40. The department of Malargüe isn't the best known in Argentina, and its scenery is not particularly spectacular, but it's an interesting place to stop if you are on Route 40.
Malargüe's countryside is very desert like and there is not much vegetation. If you arrive in spring or summer then you should explore Reserva Provincial La Payunia which is about 150 km away in the south of the department. There are some pretty views between the red and ochre coloured rocks which are crowned with grass that has yellowed in the sun, a few rare wild flowers and timid guanacos.
If you fancy it, you can climb the Morado or Payún Matrú volcanoes to get a panoramic view. Other things to see include: Castillos de Pincheira, fortress like limestone rocks, or Laguna Llancanelo, a UNESCO Ramsar (or wetland) zone where you can see colonies of pink flamingo, and Caverna de la Brujas, old caves made for speleologists or lovers of old legends.
Desert scenery, an arid climate and wild animals - things to see in Malargüe. If you are in the region during winter then Las Leñas ski resort is only a few hours away.