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Submerged River Valley - Upper Newport Bay

Hidden : 6/27/2005
1 out of 5
1 out of 5

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Geocache Description:

This cache is located on a paved bike path a short way from street parking. This cache discusses the geomorphology of the Upper Newport Bay. The geomorphology of an area is the explanation of the events and processes that have resulted in the current landforms of the region. The following information was compiled from the sources listed at the end of the cache.

The Upper Newport Bay is thought to have formed 300,000 years ago when sea levels were lower than they are now due to a glacial period. At that time, geologists estimate that this area received about 80 inches of rain a year. This likely produced year-round flow in the ancient Santa Ana River that flowed through the channel below you and southward beneath Upper Newport Bay.

At that time, the river would have flowed though a flat flood plain. Had any of the hills you see around you today existed, the river would have taken a different course. After the river had eroded out a stable course, the Newport Mesa and San Joaquin Hills began to slowly uplift as a result of movement along the Newport-Inglewood fault zone. Flow in ancient Santa Ana River was able to maintain its course throughout the uplift by eroding the land faster than it was uplifted. This resulted in the steep cliffs you see surrounding the bay, such as the 100 foot cliffs across the bay to the east.

Rising sea levels completely submerged the bay until about 15,000 to 25,000 years ago. This submersion effectively stopped the continued erosion of the river channel as the Newport Mesa continued to rise. While the bay was submerged, the ancient Santa Ana River also found a new path emptying into the ocean at Alamitos Bay.

Recent lining of the creeks that continue to drain into the Upper Newport Bay has resulted in the filling in of the bay with more sediment than would be expected in a natural system. As a result the bay has been dredged to maintain its current configuration.

Filling in of bays is a natural process, but not at the rate that had been observed in the years since the area was urbanized. Natural processes would eventually fill in the bay, turning it into a marsh, then open grass land if allowed to continue.

Logging requirements:
Send me a note with :

  1. The text "GCPFR5 Submerged River Valley - Upper Newport Bay" on the first line
  2. The number of people in your group.
  3. What features of the drainage channel that the bridge crosses over has contributed to the speed that the bay has been filling.
  4. What features are seen in other flood control channels throughout the watershed.

The following sources were used to generate this cache. None of this cache was original work.

  • Colburn, Ivan P. (California State University, Los Angeles) THE ROLE OF ANTECEDENT RIVERS IN SHAPING THE SOUTHERN CALIFORNIA COAST, AAPG Pacific Section / SPE Western Regional Joint Meeting, May 19-24, 2003, Long Beach, California, U.S.A. (Abstract only)
  • Norris, Robert M. Robert W. Webb, Geology of California Second Edition, John Wiley & Sons, Inc. 1990
  • Text for Geology 303, Coastal Systems and Human Impacts, a CSU Long Beach Department of Geological Sciences Course,
  • Image Source: EagleAerial July, 2003

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