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A Relic Ravine or Hollow of Old California

Part 1

Also see:
 |  Part 1 - Exploring an hypothesis
 |  Part 2 - Simple treatment

Hypothesis: The prehistoric people as represented in the artifacts recorded from the famous archaeological site at Malaga Cove (CA-LAN-138) could have used stone weir technology in the nearby ravine for fresh water management purposes.


The research so far indicates the following about CA-LAN-138 and this relic ravine or hollow:

(1) There was just the minimal amount of water volume flowing down the ravine to support the needs of the various peoples represented at CA-LAN-138.

(2) The seasonal flow pattern of the water in the ravine is such as to motivate the ancients to intervene in the natural process by building stone weirs.

It's logical to conclude the ancient people there could have used stone weir technology in the hollow.

Terrain view using Google Maps. Mark-up location indication pointers added.

1902 U.S Geological Survey (detail). Mark-up location indication pointer added.

Then and Now photos

1925 Today

One aspect of the original (pre-historic) state of the canyon was, of course, it was without all the non-native vegetation present there today. Except for the remaining few sparce native plants, practically all of the flora in the canyon today is non-native, including that eucalyptus tree shown in the 1925 photo. Eucalyptus trees were imported from Australia to California in the 1850's and by 1902 were all over the place.

Ironically, the thick non-native brush currently in Malaga Canyon, while disruptive in many ways, has created a type of buffer to human activity, particularly a buffer to human activity near and at the bottom of the canyon.

Malaga Canyon with jurisdictions today

Malaga Canyon with jurisdictions today and contours

Excerpt from the book, "The Rancho San Pedro" (Published in 1961), sub-chapter on "Agricultural Activities":

"On the far western side of the Rancho San Pedro, the fresh water supply is in marked contrast to the riverbottom lands on the east. Along the ocean front and immediately east of the City of Redondo Beach, the land was sandy and almost completely arid. Near the Palos Verdes Hills to the south, an occasional spring was the only source of good water, generally being inadequate in meeting the needs of cattle and sheep. The ownership of water holes was a continuing cause of friction between the Dominquez and Sepulveda families. Victor Carson, a direct descendant of Manual Dominquez, recalls that the trampling of the stock around the few springs often clogged the openings with mud, making it necessary to clean them out regularly. As a result of the water shortage, very little farming was carried on in that area until later years. Following the serious drought period of 1862-65, which dried up most of the springs, the drilling of wells gradually solved the water problem and made additional acreage available for cultivation."

"The Rancho San Pedro", by Robert Cameron Gillingham.

Analysis: The "occasional spring was the only source of good water" might be describing Malaga Canyon and/or White Point.

In either case, Gillingham's interview with a direct descendant of Manual Dominquez is interesting because of the memory of the water flow pattern of the area. I think this conversation record is consistent with the observation that there was just enough water flowing down the canyon to support the fresh water needs of the pre-domestication of plants and animals cultures and just the type of flow pattern to motivate them to intervene in the process by perhaps building stone weirs in the canyon. Likewise, not so much water flowing to support the activities of the later post-domestication of plants and animals cultures of the Spanish, Mexican and American peoples and apparently not enough to motivate them enough to develop the canyon to exploit the resource in a manner that probably would have destroyed the canyon.

Screen shot of EPA online map showing calculation of Malaga Canyon rainfall catchment area = 916.505 acres.

Determination of a reasonable estimate of the amount of natural water flow volume in Malaga Canyon:

a) Catchment area = 916.505 acres
b) Annual average precipitation at Rancho Palos Verdes = 13.17 inches
c) Rough rule of thumb for calculating rainfall runoff volume on a catchment surface: "You can collect 27,000 gallons of water per inch of rain falling on 1 acre of catchment surface." Per 'Rainwater Harvesting for Drylands and Beyond' by Brad Lancaster.
Math: 916.505 x 27,000 x 13.17 / 365 = 892,876
892,876 gallons per day (on average) of water from natural sources flowing down Malaga Canyon into the ocean.

The flow pattern when distributed across the 12 months of the year starting with December forms roughly a bell curve type pattern. The flow peaking in June and July, the summer months - "when it would be needed the most" by the people represented at CA-LAN-138. This analysis by Allan Rigg, City of Palos Verdes Estates, Director of Public Works & Planning.

The percentages in the above chart I created are ballpark numbers, roughly based on the well level data from various geology engineering reports analyzing the persistent artesian groundwater flow problem in the commercial buildings at Malaga Plaza.  The cause of the distribution peaking is the summer is the well-studied aquifer on Palos Verdes hills in the catchment area of Malaga Canyon. The aquifer has very fine sand in it which effects the transitivity of the rain water falling on the hills. The water moves slowly through the fine sand in the aquifer before it reaches the canyon. The rainy season is from late December through April. The flow water is delayed as it travels through the earth to the canyon. Possibily explains conflicting observations about whether the water flow down the canyon was/is persistent or intermittent.

Water flow volume - 2009/12/13 3:00PM

Rough field measurements and very rough calculations of water flow volume at the spot in the canyon just before the stream empties out into the ocean. Volume worked out to an average of 230,860 gallons per day.

With the model of the average monthly distribution of natural water flow down Malaga Canyon in Flow 4, assign percentages of the annual total flow for each month. For instance, July is 12% and December with 5% of the natural water annual flow volume. Now, assuming December is 5% – December, then works out to 545,000 gallons per day per the model. So, the field observation on 2009/12/13 indicating 230,000 gallons a day, isn’t all that far off the model number – considering all these are very rough estimates given rough assumptions.