RUST TO RUST -- LIMONITE AND EARTH CHEMISTRY

Next to an arroyo along the west side of the road, heading north of Rueben's toward the Technical School, are exposed beds of friable, dirty-looking, yellow-brown limonite, an amorphous (formless, i.e., no crystals) ferric hydrate, which is sometimes an iron ore.  These can also be found next to the twisted bedding north of Serenity Beach and on Calzada Chetumal down from the old cemetario.

San Felipe Beach Shelf

North of Rueben’s – Home of the infamous “Coco Loco”

This indicates that this section of land was once below the fresh water table, quite some time ago.  Geologically recent peninsular emergence has now pushed it twenty feet above sea level and, therefore, far above the local fresh water table.  The beds are now exposed in a wash.  An alkaline environment (i.e., high pH or "basic") is required, which is what desert ground waters generally are.

So-called "red beds" -- accurately named iron oxide pigments that make the red rocks of Sedona, for example  -- are associated with evaporates – not under water -- in an arid, desert environment.  Iron oxide, Hematite, forms after deposition owing to in situ ("in-place") alteration of the iron-bearing sands.  Progressively older deposits disclose successive stages of development of hematite staining in red beds that evolved from originally non-red iron-rich sediments.  This is most apparent in arroyos and wash cuts through alluvial fans.

Calzado Chetumal – North Side

Iron silicate minerals (FeSiO₃) and black micas (Biotite flakes and “books”) are found in all local beach sands.

Iron-Rich Slab – South of Technical School

Exposed Beds – Wash South of Technical School

The local sands are derived from decomposed granites which make up much of the mountains surrounding San Felipe the alternation of these common dark minerals to iron oxides (that is, rust -- Fe₃O₄ and Fe₂O₃) happens very slowly.  The rate of alteration depends upon the amount of water that moves through the meager soil overlying the basement rocks.  The unadjusted average rainfall in San Felipe is less than three inches a year and percolation is only a few vertical inches.  In the Baja this type decomposition would take place only on the surface of dissected bajadas, i.e., merged alluvial fans.  You drive over a large one heading to Three Poles.

SITE CHECK LIST

RUSTOLEUM

1.        Name                          Rust Beds
2.        District                       Technical School
3.        Address                      Various
4.        Hours                         Daylight
5.        Ambiance                   Trash (I HATE plastic!)
6.        Cost                            Free
7.        Photo Op                    Alright, I guess
8.        Condition                   Dirty
9.       Significance                Chemistry
10.      Time                           A minute
11.      Workout                     Easy
12.       Conclusion                 Go on to granite Quarry
13.       www                           N/A
14a.     GPS Coords:              Lat: N 31°02.179' 
            (Beach)                       Lon: W 114°49.577'
14b.     GPS Coords:              Lat: N 31°01.412' 
            (Chetumal)                Lon: W 114°50.153' 
14c      GPS Coords:              Lat: N 31°02.368' 
            (Tech School)            Lon: W 114°49.530
14d.     GPS Coords:              Lat: N 31°02.238' 
            (Wash)                       Lon: W 114°49.697

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