Great video, LowBoy. I mean from a "watchable video" perspective. Good camera work and well narrated. And of course I have no objection to the fact that our G2 is the featured beeper.
Herewith a few comments after a single watch of the flick.
1. GG Park is an amazing piece of real estate, perhaps someone will post a link to a resource which describes its history and features in detail.
2. Many years ago before I knew what a beeper was, I lived two blocks from GG Park. 47th & Judah. It is a huge park right in the middle of one of the most intensively developed metropolisses (English teachers, keep yer china clippers clamped shut) on the planet. So huge, that portions of it are "almost wild", and it's possible to dig a hole to retrieve an object without dealing with manicured turf issues. Back when I lived in SF, it was possible to camp out and live in GG park if you were clever about it, I don't know if it's still "wild" enough to do that.
3. Prior to development as a park, it was sand dunes. The developer and visionary Adolph Sutro decided that if planted to trees and shrubs and and irrigated, the vegetation would collect enough water from the famous San Francisco fog to become well vegetated with limited need for additional irrigation. And, being a good hydrologist, he realized that right there next to the beach there would be a freshwater aquifer that could be pumped with windmills powered by the same persistent westerly winds that bring the fog in. The beach environment itself afforded recreation opportunities that could be developed both for free public use and for commercialization. ........This was the era of the "robber barons" and yet in the midst of all that, there were visionaries who weren't automatically precluded from impact, even the robber barons could catch a smidgin of the vision. Sorry, those days seem to be over, nobody seems to be labeled a robber baron any more, but something invisible keeps visionaries off the table of public discourse and out of politics. A GG Park is unimaginable today other than as a legacy of a more intelligent past. That's what's happened to the world we live in. If I elaborate much further on that subject, I will be banned from this forum, so I will refrain.
4. So as you saw in LowBoy's flick, the soil in GG Park is sand with a bit of organic matter, virtually no clay to bind it.
5. The sand in GG Park is blown in from Ocean Beach by westerlies. That sand is primarily the product of granite source rocks all the way from the Sierra Nevadas to fairly local granites. Therefore its composition is quartz and magnetite. The feldspars and related silicates weather to clay minerals the transport (or lack of same) of which is driven by Brownian and electric attraction forces, and not by hydraulic shear as sands are.
6. And, the Sierras being a mere 100 miles away, Ocean Beach has gold. The problem with ocean beach gold derived from distance sources is that the stuff is so fine, it's difficult even to pan. It's been pulverized to smithereens by its tortuous voyage to the beach which may have taken tens of millions of years (or more) of cycles of erosion and deposition in many environments. I don't know if anyone has ever given a good explanation how gold from the Mother Lode can actually make it through the Bay, through the Golden Gate (a very deep and wide channel) and finally land on the surface of Ocean Beach.
7. Nonetheless there's enough gold in Ocean Beach that people eked out a living "panning" gold on Ocean Beach during the Great Depression of the last century. I think the only people who were successful to keep at it, were the people who used mercury, and weren't necessarily doing panning as we think of it. Which is why I put the word panning in quotes. Gold Beach in Oregon is a better example of an ocean beach placer, for those who care to study the subject of ocean placers.
8. And then there's the issue of magnetite. Back in the late 60's, I was only 3 blocks from the beach and of course often went beachbumming there. There were these streaks of black sand that were sticky, I thought they were oil spill residue. Until I eventually figured out that they didn't make my hands oily, the stuff only felt sticky because it was magnetite black sand sticking to itself because of its magnetic attraction and also because of its weight. I'd seen the same stuff in the Sierras as a kid but not in massive concentrated streaks like this.
9. So magnetite, being heavy, should stay on the beach and not be blown west by the prevailing winds, right? It doesn't work that way. First, consider that magnetite should not be on Ocean Beach in the first place, unless you accept the idea that magnetite is readily transportable despite its density. .......Here in El Paso, we have a large region of sand dunes, some stabilized and some not. The sand is from Rio Grande sediments and it is blown by southwesterlies up against and over local hills. The sand material comes from long distances upstream. From the standpoint of geophysical process, it's analogous to GG Park. Even from the perspective of vegetation, there's analogy. We don't get fog here, but now and then we do get rain, and many of the plants that naturally grow here are designed as rain collectors which concentrate rain toward the stem where it can percolate more deeply into the sand and thus be more available to roots and less available to surface evaporation.
10. I've taken magnetic susceptibility measurements here and there, and observed carefully by eye the distribution of silica and magnetite sand blowing on windy days when hiking, including in the hills which almost but not quite terminate the sand dunes. There are streaks of magnetite on the highest dunes. And the overall magnetic susceptibility is surprisingly consistent in the area, defying what should be the sorting mechanism afforded by the wind.
11. So, I'm sure this same phenomenon is at work in GG Park. This would mean that the magnetic susceptibility ("mineralization bars") in GG park would be moderately high, probably not more than a factor of 4 lower than the sands of the American River in Sacramento a hundred miles away.
12. However, I don't have any measurements either place. And, the hydraulic sorting that takes place on Ocean Beach would make taking an average there difficult, even if that average were about the same as in the GG park dunes.
--Dave J.
