Road Salt-:
Use a stiff brush to dislodge any loose road salt and then remove with a vacuum, spray the area with a carpet cleaner and let it soak in, rinse with an alkaline solution of baking soda / water and repeat until most of the stain has been lifted. Finally clean carpets by spraying the area with a carpet shampoo rinse and then remove with a carpet extractor. Using the vacuum, remove the excess moisture, loose dirt and the grime. Allow carpets / mats to thoroughly dry before use, then apply a fabric protection (303TM High Tech Fabric Guard)
Be aware that once you add water to salt it becomes acidic (corrosive); "Always add the acid to the water, never add the water to acid" Chemistry 101, take care to dry the affected area thoroughly after the salt has been removed.