The theory of the light meter still governs even a digital camera.
White, when metered, reflects 36% more light than the grey card, upon which exposure is based. That is a 2 stop correction.
The salt is very reflective. Contrast, on the shadow side, can be way less than is generally the case. If the automatic
exposure camera reads any subject that is darker than white, it will give an adequate exposure. If the reflectance from the
salt influences the exposure, you will be under exposed. An incident meter will show the normal exposure to be 3/4 to 1 stop less than at sea level. You are at 4300 feet and there is very little pollution out there. But, that is different than the white giving you an underexposed image.
It's just like tuning a fuel system. You have to know something about what you are doing but with digital cameras,
programs are available to bail yourself out when you don't know what you are doing.
The nice thing about auto exposure cameras is that if they mess up it's generally in the same direction all the time. Correction is not a huge problem.
Just shoot away. Someone can bail you out if u made mistakes.
FREUD