Eastern Mojave Vegetation U. S. Highway 91  
 

Tom Schweich  

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 For the most part US Highway 91 has been replaced by US Interstate 15. There are two segments of US Highway remaining. A northern segment follows a route abandoned by I-15 from just south of Pocatello, Idaho, through Logan, Utah, and then into the Great Salt Lake basin, where I-15 is rejoined. The southern segment of US Highway 91 heads west from Saint George, Utah then turns south to Littlefield, Arizona, bypassing the route that I-15 now takes through the Virgin River Canyon.
 
Northern segment of US Highway 91 is below.

Other articles: Interstate 15 Idaho Exit 36  

Junction: US Interstate 15, north to Pocatello, Idaho, or south to Salt Lake City, Utah.

The reason to take US Hwy 91 south rather than I-15 would be to view the spillway of Pleistocene Lake Bonneville into the Snake River drainage at Zenda and Red Rock Pass.

 

 

Literature Cited:
- Hart, William S., Jay Quade, David B. Madsen, Darrell S. Kaufman, and Charles G. Oviatt., 2004.

Locations: Zenda.  

Zenda

Location in southern Idaho, off US Highway 91.

Zenda is given as the location of an alluvial dam that held the highest stand of Pleistocene Lake Bonneville for 500 to 1000 years before it eroded, creating the Bonneville Flood.

Other articles: Field Notes 21 Oct 2017
Full Size ImageView south to Red Rock Pass
Full Size ImageLooking north towards Zenda (in the trees)  

Stopped at a little hill between Zenda and Red Rock Pass.

 

 

Literature Cited:
- Hart, William S., Jay Quade, David B. Madsen, Darrell S. Kaufman, and Charles G. Oviatt., 2004.

Other articles: Field Notes 21 Oct 2017

Locations: Red Rock Pass.  

Red Rock Pass

Full Size Image
Hill with monument
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Interpretive Panel for Red Rock Pass
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Interpretive Panel for Red Rock Pass
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Memorial plaque to Captain Jefferson Hunt
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View from top of hill
Bedrock threshold for the Provo shoreline of Pleistocene Lake Bonneville.

Red Rock Pass Geological Site

About 14,500 years ago, ancient Lake Bonneville overflowed at this site. A dam of alluvial fans between Oxford Mountain to the west and the Portneuf Range to the east suddenly eroded releasing Lake Bonneville from the Great Basin into the Snake River system. The Peak flow was about one million cubic meters per second at the pass, or about 500 times the maximum discharge on the Snake River at Idaho Falls, Idaho. Ancient “bathtub ring” shorelines up to 1,000 feet above the valley floor are readily visible in the Salt Lake Valley. Evidence of the flood is visible thoughout southern Idaho with areas of scoured bare bedrock (“scabland”) and deposits of boulders (“melon gravel”) marking the flood path. After about 11,000 years, Lake Bonneville receded to become the Great Salt Lake. Highly saline and only 40 feet deep, it is but a shadow of giant fresh-water Lake Bonneville.

Red Rock Pass is the geographic northern extremity of the Bonneville drainage basin, and was also designated by the early Latter-day Saint leaders as the northern edge of the proposed State of Deseret. North of here, water flows to the Snake, Salmon, and Columbia rivers, on the way to the Pacific Ocean, but south of here it flows into the Great Basin and the Great Salt Lake.

South of the monument in Red Rock Pass, the house-sized limestone blocks were jostled during the breakout of the Bonneville flood. The uneven topography northwest of the monument is a landslide which flowed into Red Rock Pass after it was deepened about 400 feet during the flood. Ancient cave formations are found in the flat-lying limestone of Red Rock Butte immediately north of the monument.

Red Rock Pass

You are standing in the outlet of ancient Lake Bonneville. A vast prehistoric inland sea, of which Salt Lake is a modern remnant.

Covering over 20,000 square miles when it overflowed here about 14,500 years ago, its winding shoreline would have stretched from here to New Orleans if it were straightened out. This pass was deepened considerably when Lake Bonneville began to slow into Snake River. For a time, a torrent several times larger than the Amazon was discharged here. Finally, with a hotter, drier climate that slowly emerged about 8,000 years ago, Lake Bonneville gradually disappeared.

No 119

Erected October 2, 1950

Captain Jefferson Hunt, Soldier, Pioneer, Churchman

Charles Jefferson Hunt served in the Mormon Battalion as captain of Company “A” and as assistant executive officer, in its historic march from Council Bluffs, Iowa to San Diego, California, 1846-47. His service won the commendation of all who served with him.

Under appointment by President Brigham Young in 1851, Captain Hunt was guide for the pioneers to San Bernardino, California. His pioneering service included also Provo, Parowan, and Huntsville (which bears hus name), in Utah, and Oxford, Idaho.

A convert to the church of Jesus Christ of Latter-Day Saints he was loyal, obedient, and faithful to the end.

Erected by descendents of Captain Hunt and the Utah Pioneer Trails and Landmarks Association.

  Idaho Above.
Utah below.

Other articles: U. S. Hwy 89 at W. 400 N.  

Intersection: W. 400 N., US Highway 89, east toward Bear Lake.

 

 

Locations: Logan.  

Logan

W. 300 N.

 

 

Locations: Logan.  

Logan

 
  East and West Center Street
  Intersection: South Main Street, Utah Highway 165, Southern Cache Valley.

Other articles: U. S. Hwy 89 at US 91S  

Junction: US Highway 89, south to Salt Lake City, Utah, or north to Logan where the routes diverge.

 

 

Other articles: Interstate 15 Utah Exit 364  

Brigham City

Junction: US Interstate 15, south to Salt Lake City, Utah, or north to Pocatello, Idaho.
  Northern segment of US Hwy 91 above
Southern segment of US Highway 91 below.

 

 

Other articles: Interstate 15 Saint George

Locations: Saint George.  

St. George

  • Junction:
    • US Interstate 15, North to Salt Lake City, South to Las Vegas.
  •  

       

    Santa Clara

     

    Literature Cited:
    - Retallack, Gregory J., 2009.

    Locations: Ivins.  

    The town of Ivins is just to the northeast of the highway.

    Just to the northeast of Ivins is a paleosol collection site in the Triassic to Jurassic Chinle, Moenave, and Kayenta formations used by Retallack in his 2009 study of greenhouse crises of the past 300 million years. Retallack used stomatal index data for fossil Ginko and related leaves as a proxy for past CO2 spikes and paleosol chemical data as proxies for temperature and humidity changes. These data show that global warming due to CO2 rise is a not a unique event in earth history and that the magnitude of the coming anthropogenic greenhouse pales in comparison with past greenhouse spikes at times of global mass extinctions.

     

       

    Shivwits

     

    Other articles: Gunlock Road at Old US Hwy 91  

    Junction: County Route 3184 "Gunlock Road"

     

     

    Other articles: Mojave Desert Joshua Tree Road at US Hwy 91  

    Junction:

    Junction: Mojave Desert Joshua Tree Road to area where Frasera albomarginata was found.

    Other articles: Beaver Dam Mountain Road at old US Hwy 91  

    Junction: Beaver Dam Mountain Road

     

       

    Utah Hill Summit

     

     

       

    CastleCliff

     

     

     

    Other articles: Mojave Desert Joshua Tree Road at US Hwy 91  

    Junction:

    Junction: Mojave Desert Joshua Tree Road
      Utah above
    Arizona below

     

     

    Other articles: Interstate 15 Littlefield  

    Littlefield

    Junction:
    • US Interstate 15, north to St. George; south to Las Vegas.

     

     

       

    Literature Cited

      A list of all literature cited by this web site can be found in the Bibliography.
      Hart, William S., Jay Quade, David B. Madsen, Darrell S. Kaufman, and Charles G. Oviatt. 2004. The 87Sr/86Sr ratios of lacustrine carbonates and lake-level history of the Bonneville paleolake system. GSA Bulletin. 116(9/10):1107-1119.
      Retallack, Gregory J. 2009. Greenhouse crises of the past 300 million years. GSA Bulletin. 121(9/10):1441-1455. {TAS-pdf}
    If you have a question or a comment you may write to me at: tas4@schweich.com I sometimes post interesting questions in my FAQ, but I never disclose your full name or address.  


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    Date and time this article was prepared: 12/12/2017 5:58:01 PM