Friday, December 22, 2017

Answer: What are those light patches on the ground?

You'd think this is easy.. . 

But in fact, answering a simple question like "What are those light patches on the ground?" turns out to open up a huge can of worms.  I spent waaaay too long on this (but had a lot of fun in the process).  

As you remember, on a recent flight back to San Francisco, I was traveling northward over Santa Cruz and noticed several distinct light patches on the earth below.  Here's a map of the light patches I saw.  (I actually noticed a bunch, but let's start with just these. Once we figure out how to identify such features, you can go back to the original map and start identifying other features that YOU notice when flying.)   


1. What ARE those light patches on the ground? 

2.  Is there any reason that they would be in a line like this?  What's special about this particular are that would cause light patches like this? 

To get you started, the patch on the far left of the image is at:  37.029531,-122.153212 , while the patch on the far right of the image is 37.0635053,-121.9324645

Here's what I did... 

First, I opened up Google Maps to this region, using the lat/long up above as guidance.  In Google Maps, you can put the lat/long into the search box and create a map like this:

Map #1

If you switch to Satellite view (by clicking on the Satellite image in the lower left corner) you can quickly slide the map around until it looks exactly like the map with the patches on it. 

Map #2

As you probably figured out by now, I used Google Earth to create the first original map (the one with the yellow dashed line), and when you look at this place in Google Maps, you get a lot of additional information. (I made the original map in Earth because I could turn off all of the slightly distracting city names and roads.)  

Of course, with this view in place, you can zoom in and out to figure out what each of these patches is.  

When I zoomed into the first location (Map #2 with the red balloon), you can see that it's a quarry of some kind.  

But what KIND of quarry is it?  Who owns it? 

To find this out, I did two things.  

First, I did the obvious query: 

     [ quarry Bonny Doon Road ] 

which led to some great results, including this text by a quarry fan (yes, there are such things!) which lists some quarries in the area--including the name of this quarry... unsurprisingly, Bonny Doon Quarry, which mines limestone.  

Oddly, the information block about the quarry looks like this: 

Mine name: Bonny Doon Limestone & Shale;
Operator: RMC Lonestar;
Address & County: 700 Hwy. 1, Davenport, CA 95017, Santa Cruz County
Latitude: 37.03, Longitude: -122.15
Mine location number: Map No. 728; Mineral commodity: Limestone.

When I put that street address (700 Hwy 1, Davenport), it looks like this place is quite a ways west of the quarry.  

Curious, I looked at the Streetview of the road that leads from the quarry to Bonny Doon Road, where I saw this: 

There's a road there, but more importantly, that's a crushed rock transport line, used to move crushed rock from once place to another. But where does it go?   

If you zoom out and look at the larger picture, you can see that the transport line goes from the quarry (on Bonny Doon Road) to the cement plant on Highway 1.  Interestingly enough, it seems to pass through another, smaller quarry on the west side of Bonny Doon Road.  

My second approach was to search for actual property information. Now that I know it's in Santa Cruz county, I can search for the county property map service (which many counties offer as a public service).   I used the query: 

     [ Santa Cruz country property maps ] 

which took me to the Santa Cruz county online GIS (Geographical Information Systems) search service.  In particular, I used their mapping service to search for information. It's a little obscure to use, but you pan/zoom to the quarry location, then click on the red "I" icon, then click on the quarry to get this information:  

Curious about that transport line, I then clicked on the map to the west, where the line runs.  Guess what?  They're connected... 

So now we know that this is the Bonny Doon limestone quarry that feeds crushed stone to the Davenport Cement plant, which they then turn into cement.  

Okay... what about those other "light patches"?  Are they also quarries? 

To figure this out, I downloaded the original image (the one with the red arrows), and then made my own Google Map to organize all of my notes (visit: to create your own map).  

Here, I just dropped pins at each of the light patches (and including one extra one that I found near the bottom of the area shown).  

I made this map to organize all of my notes about the light patches. LINK to the map. 

We know that the blue pin on the far left (1) is the Bonny Doon limestone quarry.  What about the others? 

This is just a regular Google Map, so if we zoom in on the pin just to the right of Bonny Doon (pin #2), we see this: 

Based on what I see here, I'm willing to bet that this is the Felton Quarry.  Let's test this idea with the query: 

     [ Felton quarry ] 

leads to (first result!) an incredibly handy document, the Santa Cruz County list of quarries!  And, to my surprise, the first picture in that document is of the Bonny Doon quarry, with a comment that the..
"Bonny Doon quarry...  mined marble and shale for the production of cement at the Davenport Cement Plant... The mine ceased operation in 2009... The mine contains hard rock mining and crushing equipment, maintenance shop, office, rock storage silos, and a belt conveyor that travels approximately 3 miles to the Cement Plant. These facilities have not been removed." 
With this great resource it doesn't take long to find that this place in the picture above is the Felton quarry, operated by Granite Construction Company which mines granitic rock for construction aggregate.

Let's do the next quarry, working our way down from the top of that column of 3 blue pins (#3).  When I zoom into that: 

It's easy to see from the brown business label that this is the Quail Hollow quarry operated by Graniterock. That county document tells us that they (despite their granitic name) actually mine sand from the Santa Margarita Sandstone for construction and industrial uses. The quarry has a sand processing plant and bulk sand dryer. (Who knew that the sand would be wet?)  

What about the next light patch (#4, slightly down and to the right)? 


The only quarry in the list that matches this is the Geyer Quarry (at the foot of Geyer Road, which comes in just from the right hand side of this photo.  

And pin #5?  Again, if you zoom into that location, you'll see this:    

The only quarry that fits this description is the Hanson (Kaiser) quarry, described as: 
"...operated by Hanson Aggregates mined sand from the Santa Margarita Sandstone for construction sand. The mined area encompasses approximately 200 acres. The mine ceased operation in 2003. All former mineral processing facilities have been removed and disturbed areas are being reclaimed to open space with a native species vegetative cover on the disturbed lands similar to naturally occurring habitats in the surrounding area. The mine is located within the sensitive Sandhills habitat west of the City of Scotts Valley."
I was curious about why this site had two names--Hanson (Kaiser)--so I did a little more digging. The query: 

     [ Kaiser sand quarry ] 

led me to several documents (fascinating reading!), but the one that was most useful was the Sandhills Conservation and Management Plan (2004) that explicitly mentions Kaiser's Felton sand quarry and the Quail Hollow quarry as having sand from: 
... the marine deposits of the Santa Margarita formation that give rise to the unique sandhills communities also provide sand that is a highly valued commercial product for several reasons. First, the sand deposits extractable from the sandhills are very deep (Section 2.3). Second, unlike cemented sandstones, the Santa Margarita formation is loosely consolidated and thus readily quarried. Third, the action of ocean currents millions of years ago sorted the particles of sand according to their size, rendering the material well sorted for its various uses. The coarse sand is valuable for construction, as it well worn (rounded) and therefore less abrasive to machinery and cause less friction when creating concrete. Unlike beach sand, sandhills sand has a neutral pH that renders it useful for burying utility cables that would otherwise be corroded by the basic pH of high salinity beach sands. These coarse sands are also used in golf courses. 

So these three sand quarries are all part of the Santa Margarita sandhills formation, which explains why they're all in a line.  

That's 5 quarries down. Two more light patches to go. 

From that master Quarries of Santa Cruz County document, it's clear that the light patch on the far right side must be the Olive Springs Quarry.  (Google Maps handily labels it as such.)  


Here, the mine is "operated by Olive Springs Quarry Inc., which mines gneissic granodiorite (granitic rock) for construction aggregate. The mine contains a rock crushing and aggregate processing plant, and an asphaltic concrete (AC) plant. The permitted mining area encompasses approximately 48 acres and is permitted to operate until at least 2044..."

There's one more light patch to explain:  patch #7 in the above photo.  Again, zooming in, we see this: 

Patch #7

Ah.  This isn't a quarry at all, but a lumber yard.  But could it have been a quarry in the past?  

You can click on the 3D button in Maps to take a sideways view of this location.  Below I've made a side-by-side illustration of the lumber yard and 2 other quarries.  Note how the quarries are all built into the sides of hills with lots of staircasing, while the lumber yard is on the flat part.  

Quarries can be built on flat land, but in this part of the world, the quarries are typically dug into hillsides.  

Now we know what everything is: 
#1:  Bonny Doon quarry (marble and shale to make cement)
#2:  Felton quarry  (granitic rock)
#3:  Quail Hollow quarry (sand)
#4:  Geyer quarry (sand)
#5:  Hanson (Kaiser) quarry (sand)
#6:  Olive Springs quarry (granitic rock)
#7:  San Lorenzo lumber yard
How would we find out if there's a reason for all of these quarries to be located in such an interesting linear layout?  

Let's look for a geology map of Santa Cruz county.  (Tip:  Such maps are often created by the state, the federal government, but are always labeled by county.) 

     [ geology map Santa Cruz county ] 

which leads us to a lovely Geologic Map of Santa Cruz county.  Here's the relevant part: 

I want to overlay this map with the original image to see if there's any relationship between the geology (e.g., the Santa Margarita sandstone) and the location of the quarries.  

There are lots of ways to over translucent overlays of images, but one fast way is to create a new Powerpoint presentation, import the image (in this case, the geology map above) and then import the original "light patches" image and make that translucent.  (In Powerpoint, you select the image and use "Format Picture," selecting "Picture Transparency" to do this.  In Google Slides, do the same thing, but select the top picture, then Image Format>Adjust Image>Transparency.)  

This is the overlapping illustration I made: 

With a little playing around with the transparency controls, you can figure out that quarries #4, 5, 6 are.  Turns out that they are part of the tan colored region which are "middle miocene sedimentary" rocks.  

What are those "middle miocene sedimentary rocks" at the Quail Hollow (4), Geyer (5), and Hanson (6) quarries? 

A search for: 

     [ middle miocene sedimentary rocks Santa Cruz  county ] 

leads to a report on the "Stratigraphy, Paleontology, and Geology of the Central Santa Cruz Mountains, Central California Coast Ranges" (a Geology Survey paper published by the Department of the Interior).  In this document we learn that there are several layers of sandstone here, one of which is the Santa Margarita sandstone that's quarried from these locations.  The stone is described as "yellowish-gray to white sandstone," which lines up with what we see in the aerial photos.  

From "Stratigraphy..." page 8, figure 2. 

Harder to see in this illustration is the location of the Bonny Doon quarry:  

This part of the geologic map shows this to be "metamorphic" rock.  If you look up [metamorphic rock] you'll learn that these are rocks that have been transformed under heat and pressure to... things like marble and slate.  (Which is what was mined at Bonny Doon.)  

Doing this same analysis for Felton quarry (#2) and Olive Springs (#6) shows us that they're mining granitic rocks, just as the quarry summary tells us. 

The geology map is the key to understanding what's happening with the "light patches"! 

FINALLY... we understand what's going on here.  

There are several quarries that tap into the Santa Margarita sandstone formation (Quail Hollow, Geyer, and Hanson).  Since that formation runs roughly vertical, it makes sense that the quarries would run roughly north-south.  

The Bonny Doon quarry, however, is mining marble and shale--and there just are not that many outcrops of this type of rock.  (The only other sizeable area of marble in the area is found on the UC Santa Cruz campus, which mined marble to make cement, just as the Bonny Doon quarry was. And yes, there's an old quarry there too.)  

Both the Felton and Olive Springs quarry are excavating granitic stone, both in small, localized areas of granite.  

So the "alignment" of Bonny Doon, Felton, and Olive Springs on an east-west axis is just an accident.  There's no outcrop of a particular type of rock that causes them all to line up.  

Search Lessons

This post has gone on plenty long--sorry about this, but there's SO much to cover!  Let me sum up with a few search lessons... 

1. Use multiple resources to pull together information.  As you can see, I used old newspapers, images from satellite photos, and even the 3D structure of the landscape to figure out what's going on.  This wasn't a simple "look up the answer" kind of question.  It was a simple question prompted by looking out of the plane as I overflew the area.  But getting an understanding of why those patches lined up took quite a bit of digging.  

2.  Pay attention as you read--you'll often find the answers to related questions in related documents.  As I was looking for information about the Felton quarry, I found a lot of information about Bonny Doon and all of the quarries that I hadn't yet realized I was looking for!  

3.  Stay organized. In this Challenge, I was grabbing information from all over the place.  I ended up creating a MyMaps map of all the light patches and quarries to keep track of them all.  

I don't know about you, but this was an all-consuming SRS Challenge.  All told, I spent about 8 hours writing up this answer.  (And I didn't include all of the interesting side-tracks I went down!)  But I hope you picked up a few online research skills along the way.  

I'm taking the next week off, but will return in the first week of 2018 with a new Challenge! 

Search on! 



  1. Thank you Dan,
    I learn something new from your search question every week, but this one was especially useful as I am a bit of a Google map nut. I am always looking up places mentioned in the news.
    Thanks for putting in those hours and writing it all up.
    Have a Kool Yule to all!

  2. And i will use this example (with full attribution) in a talk I am about to give to a conference of Digital Librarians from all the campuses of the University of California. These are the skills that the libraries ought to be teaching our students, I will say.

    Happy New year, Dan.


    1. Thanks, Don! These are *exactly* those skills that we need to be teaching. Happy New Year to you as well!

  3. nice endorsement… all over limestone/data – mining/digging/sifting/sorting… curiosity - wonder, suss & confirm.
    site (Don needs to update his social media - G+ for example… or not)
    TED example
    a different 'norman'
    all about $$

  4. Brilliant detective work Dan, I really like this one. jon tU

  5. Replies
    1. Good Morning & Good day! I just want to wish to Dr. Russell and everyone of us in SearchReSearch the best and happy New Year 2018. I am sure we will find incredible things and learn millions of new things this year with each challenge.

      Happy New Year!