Roma: Bluffs, Landmark, Rio, Ford EarthCache
Roma: Bluffs, Landmark, Rio, Ford
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Geo/EarthCache Description Welcome to the Rio Grande Valley and the famous Roma Bluffs. This is not your typical geocache; it is an EarthCache. Instead of looking for a "cache container" you will be brought to a geological feature. For this EarthCache the geological feature is the Roma Bluffs.
ABOUT THIS LOCATION The site of the coordinates is located in Starr County in southern Texas near the Rio Grande River in the City of Roma and is in the vicinity of the intersection of Convent Ave. and Water Street. This is a daylight only cache. Parking is available. This EarthCache pertains to the natural landmark here, the Roma Bluffs. These are bluffs! Please be cautious; remain near the curb and on the road side of the fence.
GEOLOGICAL INFORMATION ABOUT 38 million years ago this area was the eastern coast where the land met the waters of the Gulf of Mexico. The region of meeting formed a crescent or tilted C-shaped deposition through Texas called the Jackson Group. Of the three stratigraphic units of the Eocene Epoch (an epoch of the lower Tertiary Period), the Jackson Group is the youngest unit; its beginning is dated at 38 million years ago, and it ended 36 million years ago. This unit basically consists of a number of layers that are either sand or clay dominated with the most sand content being here in South Texas. The Jackson Group consists of four formations which are from oldest to youngest, Caddell, Wellborn, Manning, and Whitsett formations. Marine extinctions divide these formations. Thus, the Jackson Group contains some marine fossils and marl beds as well as lignite and glauconite.
LOOKING at the bluffs it may be difficult to visualize that the Jackson Group is 360 feet thick here in South Texas. It increases to 875 feet thick in South Central Texas and then decreases to a low of 310 feet in East Texas. The Jackson Group in East Texas is shown on a chart to be buried 15,000 feet beneath younger rocks and sediment. In a region of South Central Texas there are large piles of earth which are from former uranium mines in the Jackson Group as well as exploration for oil and gas. The bedrock from the Falcon Dam exit to Garceno, which is several miles east of Roma, is the sandstones and claystones of the Jackson Group. These sediments were brought here from the Rocky Mountains and other places by the Rio Grande River.
THE Roma Bluffs here extend for 800 feet along the northern bank of the Rio Grande River and is the southern terminus of the Jackson Group. The bluffs kept the river on a stable course here compared to its numerous course changes further downstream with its many resacas/oxbow lakes. On either side of the Roma Bluffs is an arroyo, Arroyo de los Negros to the right and Arroyo Roma to the left. There also is an arroyo across the river. The arroyos provided access toward the interior of both countries. These Roma Bluffs are a famous historic landmark that has helped people for many centuries locate the ford here so they could more safely cross the river. From the 1850s to 1907 steamships went from Brownsville to Roma and back! Roma Bluffs is on the southern boundary of the Roma National Historical District. There also is an overlook here for additional views. Enjoy this great site!
EARTHCACHE INFORMATION To receive credit for this EarthCache please answer the following questions. ( You do NOT need to wait for a confirmation from the EarthCache owner before logging your find. Please make no reference to your answers on that log; send your answers only to the EarthCache owner.)
Questions: 1. (Optional) Take a photo of yourself/group with GPS near coordinates and perhaps another of a view you could not resist! Although photos are now optional they are appreciated. 2. I estimate the bluff is ______ feet high, and the elevation at the top of the bluff here is _____ feet. 3. This sandstone, part of the ______ Group of the ______ Epoch with an age of about ____ million years, is a ________ color. 4. To the right a part of the bluff extends outward. Do NOT go near it. Why do you think the water did not erode this sandstone outcrop as quickly as it did the sandstone on either side of it?
Additional Hints
(No hints available.)