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Solar Project May Damage 'Significant' Fossil Deposit

Desert mountains near Rio Mesa | Photo: Benson Kalahar/Flickr/Creative Commons License

A 500-megawatt concentrating solar power station planned for eastern Riverside County may pose a risk to what scientists are calling a "significant paleontological resource," but the developer is objecting to agency requests for more study of the deposit.

The Rio Mesa project, proposed by solar developer BrightSource for 4,070 acres of private land above the west bank of the Colorado River southwest of Blythe, overlaps a fossil deposit of unknown size where hundreds of vertebrate fossils have already been found. California Energy Commission (CEC) staff have asked the company for more information on the possible impact to paleontological resources. But BrightSource has demurred, saying that exploratory digging in the fossil deposit to determine its size would slow down the project and cost them money.

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BrightSource is building a 392-megawatt power plant in the Ivanpah Valley, and has proposed yet another in California west of Pahrump, Nevada.

According to scientists at the paleontological consulting firm URS, based in La Jolla, by late spring the site had already given up more than 700 vertebrate fossils dating to the beginning of the Late Glacial Maximum, about 13,600 years ago. In the words of a February 2012 URS report provided to the CEC by BrightSource;

[T]he site contains Holocene and Pleistocene sediments, some of which produce significant paleontological resources. They reported that these are particularly concentrated in paleosol that produced approximately 650 Pleistocene vertebrate fossils, and that recovery, preparation, reporting, and curation of these fossils was ongoing. Since those reports were written, the number of vertebrate fossils identified grew to 735. Approximately 75% of these are unidentified bone fragments. Tortoise fossils (bones and eggshell) constitute 21%; rabbit fossils account for only 3%. In addition to a badger skull and mandibles, there are lizard, snake, and bird bones as well as fragments of deer antler, proboscidean ivory, and horse teeth.

URS's report continued;

Overall, the project is not expected to impact significant or unique paleontological resources because these resources have been recovered and are being curated. However, buried paleontological resources that have not been previously identified could be encountered during the project construction phase and may be encountered during ground-disturbing activities.

On February 27, CEC staff made formal requests for more data on the site's paleontological resources, including the extent and paleontological richness of the newly discovered deposit. BrightSource formally objected to the data requests in March, stating -- in CEC staff's summation -- that "the information requested was not reasonably available to the applicant without significant excavations, which would be time consuming and expensive."

The Rio Mesa plant would consist of two 750-foot power towers surrounded by more than 250,000 heliostats, anchored in place by poles driven into the ground using vibration. While the foundations of the power towers would be excavated with paleontological monitoring, BrightSource has offered no such guarantees for the vibratory driving of its heliostat poles, claiming the process would be "minimally invasive" and pose no threat to fossils. But as the CEC said in its March data request;

While the AFC provided proposed mitigation measures related to the discovery of fossils during construction excavations, there was no discussion regarding the potential significant impact to existing paleontological resources caused by heliostat pedestal installation. The insertion of heliostat pedestals using vibratory techniques will not allow the discovery and recovery of in-place fossils. Where encountered by this construction method, the fossils will be destroyed and no scientific value of these resources realized.

In March, BrightSource offered to do additional paleontological testing short of excavation, and to provide more detailed maps of the fossil outcrop. (All maps of the outcrop provided by either BrightSource or URS have been kept confidential, so as to dissuade private collectors.) However, in a summation of continuing discussions on the topic published yesterday on the CEC's website, CEC staff member Casey Weaver said

As of the writing of this Report of Conversation, staff is not aware of the status of the additional testing or report referenced by the applicant.

Vertebrate fossils are protected under a number of state and federal laws. Though the Rio Mesa project's main footprint is entirely on private land, some supporting development such as transmission connections would cross BLM lands and thus subject the project to some federal review. BrightSource has not received federal funding for Rio Mesa; if obtained, such funding would also subject the project to federal paleontological protection laws.

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About the Author

Chris Clarke is a natural history writer and environmental journalist currently at work on a book about the Joshua tree. He lives in Joshua Tree.
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