Montara Beach Field Trip Report

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MontaraBeach Field Trip Report

MontaraBeach Field Trip Report

Datafrom geological expeditions can reveal a lot about the many processesgoing on in the world at time scales ranging from millions of yearsago to a fraction of a human lifetime. For instance, rockcomposition, size, and sorting can reveal when a geological featurewas formed in addition, data such as tidal level and rate of erosionare important to geologists since they can help reconstructgeological events that occurred in the past hence enabling us topredict how geological features will behave in future. Recently, wewent on a field trip to the Montara state beach located in the SanFrancisco Bay region. The purpose of this trip was to collectgeological data that will reveal the geological history of thislocation. As such, we collected data including the composition of thebeach sand, geomorphic features of the beach and tidal levels. Thefollowing paper is a report on the field trip and a discussion of theevidence collected to show that indeed the environment around Montarabeach has changed drastically during the past several hundredthousand years.


TheMontara beach is popular for surfing, fishing as well as thebeautiful landscape. This beach is also surrounded by low hills andmountains that often attract geologists who marvel at rockformations. During our visit, we recorded data such as tidal leveland the composition of the beach sand to get an idea about the modernsetting of the beach. We established that the tidal level was rising.Also, we determined that the beach sand was moderately sorted,subangular and coarse. Granite comprised the largest percentage ofthe beach sand composition. Sediments, shells and other organicmaterial were also found on the beach.

Descriptionof Sediments

Therocks at Montara beach cliff were indigenous intrusive rocks sincethey had cooled down slowly below the earth’s surface the rockswere most definitely granite. The sediments on the cliff facecontained the minerals quartz and feldspar. However, the cliff’supper contact showed non-conformity due to the missing layers ofsediments above (table 3). The clasts were also poorly sorted andranged from pebbles to fine sedimentation. Further, the clasts werewell rounded and organized in a manner where there were layers ofpebbles and layers of fine material. This evidence when interpretedproves that the Montara beach environment is located near the faultzone (table 3).

Inanother location, the beach sand was well sorted and very fine alsothere were layers of mud and sand in the area. Further, we made theobservation that the sand was above the granite layer (table 5). Thisevidence when interpreted showed that the location was further awayfrom the fault zone and most of the sand in the area was brought bythe sea or through the wind.

Thefinal location showed a similar trend as the first location wevisited. There was more of granite than sand in the location more tothis, there were angular rocks that were also poorly sorted (table6&amp7).


Thebeach is located close to the Seal Cove fault this fault is a majorbranch of the San Andreas Fault. The fault is not well understoodsince most of it is offshore however, the fault has had majorimplications on the nearby beaches (figure 2). As faults move, theyforce rocks to move on either side in turn, the rocks form folds andsmaller faults. This is the reason for the complex and messy geologyfound at Montara beach.


Insummary, the field trip was a success since we were able to collectthe data we wanted. Data was collected data from three differentlocations and a number of differences between the locations wereobserved. For instance, we found out that most of the locations werecovered with granite sand occupied only a small part of the beach(tables 3-8). This evidence shows that the Montara beach area wasonce covered with granite. However, as time went by, the seadeposited sand on the coastline hence forming the Montara statebeach.

Figuresand tables