Upper RGV Exploring the Rio Grande Delta

The field trip to the Upper Rio Grande Valley on July 14, 2015 helped discover the vast dissimilarity between the geology of the upper and middle to lower parts of the Rio Grande Valley.  Three sites were visited to include: the town of Santa Cruz, Texas; Los Ebanos hand drawn ferry at Los Ebanos, Texas; and the sandstone bluffs at Roma, Texas.  The geology at the Los Ebanos Ferry crossing was of silt/clay like soils, fertile for trees and other flora to flourish (Figure 1).

Figure 1: Looking upstream the Rio Grande at Los Ebanos ferry crossing.  Soils here are easily eroded, notice the cut bank on the right bank of the Rio Grande.

Learned was identifying geologic features such as the limestone conglomerate rock at Loma de la Cruz (Figure 2 and Figure 3).   And also the sandstone bluffs at Roma, Texas which is a sedimentary rock similar to the formation of limestone rock (Figure 4).  These geological features have formed throughout geologic time thousands of years ago by deposition onto the Earth’s surface forming layers. 

  

Figure 2: Base of Loma de la Cruz, notice the cross at the peak.

Figure 3: On top of Loma de la Cruz is a limestone conglomerate rock.
A geodetic marker at the top of Loma de la Cruz

Figure 4:  Photo taken on top of sandstone bluff in Roma, Texas.  Sandstone is on the bottom left corner of the picture.  

The Rio Grande Valley is actually a remnant delta formed by the once highly active Rio Grande prior to damming and other anthropogenic impediments since the latter 19^th and 20^th centuries.  The water on the upper Rio Grande Valley flows into the Rio Grande watershed.  Also the effect of water on sedimentary rocks such as limestone and sandstone cause erosion to occur, which in turn breaks away matter from solid rock formations.