THE HIVE MAY 2025

Punta Chivato

As I promised last time, this month I am going to cover the Botany/Geology walk that I co-lead in March with Warren, a geologist who lives part of the year in Punta Chivato.

Punta Chivato (PC) is located about 45-60 minutes north of Mulege. To get there, it's about 15 minutes from Mulegé to the turn off at Palo Verde (unless you get stuck behind some trucks or slow poke cars on the twisty, potholed grade out of town). From the junction, after you drive down the three blocks of paved road, you hit dirt for the next 16 km. It can be rough going in parts and depending on your vehicle, comfort level and final destination at PC, it can take another 15-45 minutes. We were to meet up at El Hotelito (a small hotel and restaurant not too far from the airstrip) so it took me a comfortable, unrushed 45 minutes total to get there.

A number of years ago, Warren and I collaborated on a similar walk and we had such a great time with a small group of ex-pats from the area. This was his farewell tour and I think almost everyone who lives out in the isolated community must have shown up.

The map below shows each of the four stops on the tour and are numbered in the order described below.

Geology Notes.

I certainly learned a lot about the formation of Punta Chivato, which is a promontory with four smaller points. The area is part of a volcanic complex known as the Comondu Formation, named after the two small towns of San Miguel de Comondú and San Jose de Comondú–approximately 72 mi (116 km) almost due south of PC–which appear to be the epicenter of a gigantic volcanic field that reaches its maximum depth of about 13,000 feet around these towns and gets shallower radiating out and away.

The oldest volcanic rocks (lava) known to have originated locally in PC are from an eruption that occurred approximately 15 mya. These can be seen in the following set of images taken on the camping beach located between Punta Cacarizo andt Punta Cerrotito (see #1 on map).

In a volcanic eruption, ash particles are ejected in what is known as a pyroclastic flow that can travel at 4-5 times the speed of sound, covering the landscape in thick layers of ash. As the volcanic eruption continues, progressively larger pieces of magma (ejecta) spew from the volcano. The texture and makeup of the ash and lava that eventually comes to rest depends on the gases present at the time. In the images of the ash flow below (some from this tour and some taken in 2023), it is possible to see how different types of chemicals affected the color of the ash and how some of the molten lava and gases formed shards of glass within the layers of ash as it cooled rapidly, giving those layers a gritty texture. Volcanic cinders, larger chunks of lava, are strewn far and wide on the promontory and the general region.

Our next stop (#2 on map) on the tour was Playa la Palmita and the bluffs located near the airstrip and houses. The rock shelf (at right) and bluffs are composed of sedimentary arenaceous mudstone. The area used to be part of the sea floor and represents the second oldest rock known to have formed locally, somewhere between 5 and 3.5 mya. Dating is possible because they contain the fossils of sand dollars in the genus Scutella that became extinct after 3.5 mya. We learned that because clay particles are so fine, they are last to settle out of water and that it will only settle to the ocean floor in relatively deep water, away from the wave action occuring near shore. It is not known how deep the ocean was when these bluffs were formed. But from studies of the area, the sea level appears to have been around 200 ft higher in the distant past, explaining the limestone bluffs farther inland that rise to about that elevation (stop #4).

Our third stop of the day was not very far west from the previous one, but because of some deep ravines between the two and the lack of a direct road, the drive took about 15 minutes. After all the cars had arrived and parked, we all gathered around so I could talk briefly about the plant communities at PC as well as about what we were seeing right where we were standing...which was on an ancient seabed that had secondary gypsum deposits, embuing it with a pale gray color, and that was home to what was currently a lot of very gray, mostly leafless plants.

Warren then went on to describe how this area, extending as it does inland from the beach for about 300 to 400 meters, was formed by the constant ebb and flow of the tide over millenia. The secondary gypsum deposits arrived much later, most likely on the wind and tide from Isla San Marco, located not far offshore north of PC.

With plant lists in hand, we then headed down from the bluff to the beach and over to a shallow arroyo extending from the beach dunes back up into the marine terrace. Along the way I stopped to talk about some of the adaptations of the dune plants we were seeing, mainly: Sonoran Saltbush (Atriplex barclayana var. barclayana), Iodinebush (Allenrolfea occidentalis), Alkali Heliotrope (Helioptropium currasavicum var. oculatum), and Dyebush (Psorothamnus emoryi var. emoryi).

Maybe about 75-100 meters up the arroyo, we came to a low bank composed of shell fossils. Warren explained that it was an oysterbed, with numerous layers of shells, each separated by a layer of pebbles and small stones. All of the arroyos in this area have these exposed oysterbeds. He said that each layer of pebbles/stones probably represented an underwater landslide event that smothered the oysters, after which new oysters would begin anew on top. Near the top of the exposed bank, oysters can no longer be found. The age of the oysterbed is estimated to be around 125,000 years when the sea level was about 6 m higher.

Approximately one half of the sediments in the oysterbed is comprised of the calcareous tests of rhodoliths. Rhodoliths are "unattached, calcareous nodules composed of benthic marine red algae that resemble coral...[and] they are important for creating habitat for diverse benthic communities." [Wikipedia] These coralline algae deposit calcium carbonate within their cells to form these hard nodules. There are still living rhodolith beds about 2 kilometers offshore.

Warren also talked about an unsolved mystery found in this particular oysterbed: the presence of rounded granite stones in the same layers that smothered the oysterbed layers (salt and pepper color stone pictured at right). Why is this such a mystery? His answer is: 1). the stones apparently are part of an alluvial flow that is found in a bed only about 125,000 years old; and 2). there are no known granites on the peninsula and the nearest diorite deposits (rocks very similar to granite) are located about 250 miles to the northeast in the Cataviña area, much too far away for them to have ever been carried here by alluvial action.

Our final stop of the day was located near the top of one of the limestone bluffs visible from the beach that form Mesa Atravesada (see photo above with caption that begins: "Scrub typical to the ancient seabed...". The area is accessible by a narrow road off of the main road near the inland end of the airstrip. The continues beyond where we stopped (see #4 on map), but was getting too narrow for the all of the vehicles to be able to turn around.

Some of the rocks at the very top of the bluff were darker and of volcanic origin while the limestone beds were located a meter or more below the cap. Warren said that many of the chunks of limestone in the bluffs had drill holes in them created by clams. In Spanish, cacarizo means "pocked" and Punta Cacarizo (Hammerhead Point to gringos), which was right near our first stop of the tour, is a low, flat limestone shelf that is pockmarked with these drill holes. From our lookout, we looked down into a wide valley and plain behind Ensenada de los Muertos that had also been underwater in the distant past.

Botany Notes.

There were just too many people on the tour for me to get to spend time on more than a few of the local plants as we walked, but I did take the opportunity to talk about the local plant communities and some of the basic desert adaptations that we had or would see at the upcoming stops. Later, at lunch once the tour was done, some of us discussed having a plant walk with a much smaller group in April, so at the end of the month I headed back out there to do just that. I didn't get many photos during my first trip, so I took advantage of being back in PC to get a few more to add to this issue.

Below are some more images of plants we that we saw either on the tour or the plant walk. The first four photos below are from a dry winter in February and show a number of the shrubs and perennials common to PC and the general Gulf Coast area around Mulegé. Many of the trees and shrubs tend to start blooming in April or May in spite of it being very dry.

I can't believe how fast the season has passed. Soon I'll be heading back north to the US and hopefully I'll get to see some late Spring botanical action along the way. I'm not sure yet what next month's entry will bring, so until then, Hasta pronto...see you soon.

Debra Valov — Curatorial Volunteer

For a full inventory list of this month's plants (family, latin name and common names in both English and Spanish as well as links to photos from previous posts or my iNaturalist observations), visit this page.

References and Literature Cited

Johnson, Markes E. (2002) Discovering the Geology of Baja California. Six Hikes on the Southern Gulf Coast. University of Arizona Press: Tucson, AZ.

Rebman, J. P., J. Gibson, and K. Rich, (2016). Annotated checklist of the vascular plants of Baja California, Mexico. Proceedings of the San Diego Society of Natural History, No. 45, 15 November 2016. San Diego Natural History Museum, San Diego, CA. Full text available online.

Rebman, J. P and Roberts, N. C. (2012). Baja California Plant Field Guide. San Diego, CA: Sunbelt Publications. Descriptions and distribution.

Valov, D. (2020). An Annotated Checklist of the Vascular Plants of Mulegé, Baja California, Mexico. Madroño 67(3), 115-160, (23 December 2020). https://doi.org/10.3120/0024-9637-67.3.115

Wiggins, I. L. (1980). The Flora of Baja California. Stanford University Press. Keys and descriptions.