I see that you're in Eddy Co., NM. I had a similar situation develop in Alamogordo several years ago. The snails were innocent for killing the lawn; these feed on microorganisms that grow in well fertilized situations.....until those situations change.

In Alamogordo, a couple had a very nice home and landscape that was the envy of the neighborhood. What some neighbors might have seen but not realized was how much this couple paid a local lawn care service to establish and maintain that lush appearance. When they sold the property, the new owner had little appreciation of the effort and expense and resolved to care for the landscape according to what he thought best.

In less than a year, the lush look was history and the new owner found lots of little white snail shells where the lawn died. For a while he tried various molluscides, but the lawn continued to fail. Finding even more little white snails he thought he had a moisture issue, so he reduced the watering schedule even more. He ended up with no lawn or flowers, dying shrubs and stressed trees. But he had lots of white snail shells.

If this is like your experience---it used to look wonderful but now it certainly doesn't, you may need to find out what was done to establish and maintain the landscape before you had it. Chances are the inputs for that sloped area were higher---and more complicated---than for flatter surfaces. Establishing and maintaining a lawn in a high-temperature, desert part of the state is challenging to begin with, especially when you're trying to understand what needs to be done or corrected.

You might start with a call to your County Extension office in Carlsbad-<personal data hidden>. Explain the situation, your inputs, how much and how often---and go from there.

In Eddy County, soil and water can be challenging. Both can have lots of salts in them and pH can be high. Soils are often rather thin, of variable composition and deficient in organic matter. Plantings on slopes can very difficult to establish and maintain. Understanding the challenges and how to manage them with organic matter, fertilization and watering schedules will likely make the rest of the landscape perform better, too.