Malcomb
I'm not an engineer but I'll try to explain as I see it. The salt flats is a gentle basin as your kitchen sink is. The salt washes to the low spot ( the race track location ) and self levels due to wind and water action.
If you cover the bottom of your sink with a heavy layer of salt and wet it, it will be crusty and hard. If you sprinkle the salt heavily every couple of days, the water will dissolve salt and it will flow to the low spot. The "DRAIN" in your sink and aka "INTREPIDS PUMP" on the salt. Eventually the salt at the edges will get washed away and run to the low spot and go down the 'DRAIN / INTREPIDS PUMPS' and the area of salt gets smaller and the salt at the center "Race track" gets thinner. If the area is reduced by half , the depletion rate for what is left doubles. As the salt in your sink gets smaller and thinner but the amount that goes down the "DRAIN / INTREPIDS PUMPS" stays the same, the rate will seem to increase depletion to the extent there is no salt left. "ABOUT" where we are now.
Heavy rains some years accelerates the problem which has been happening for decades. Finally the only salt that's left is at the low spot and thin, "NOW". In my estimation the salt we have been racing on did not come from under ground deposits as some would have us think. If you stand on the salt and look all around at the mountains, you can see the ancient water water level way up on them. When that water evaporates (due to "HOLY COW" ) global warming, thousands of years ago, the salt left was on the surface. The people, not sure there,s intelligent life, that are investigating the salt loss by coring, in my estimation, have no clue.
I wasn't there but it is my understanding that when the old timers are talking about the salt being "feet thick", they are talking about the UPPER CRUST of salt. Why would they give a crap about what layers lie under and in what order. Mickey ran 24 hour endurance trials on the salt on a IIRC a 20 mile circular track. Guarantee you, that couldn't have been done since I've first went to the salt in 74.
I'm sure before they first started mining, way back when, they took core samples or at least bore holes to find out how much material was there to see if it was worth mining. Would love to see the results of those cores. Probably had them destroyed so nothing can be proven against them. Notice the conspiracy theory?
I'm upset because we can't race and may never be able to again (not holding my breath) but I'M p!ssed off that an industry with their political contributions to corrupt politicians can destroy a National Landmark.
End of rant. Back to your regularly scheduled whatever.
Ron