On Mon, 10 Aug 2020 10:42:17 -0700, Jeff Liebermann
wrote:

On Mon, 10 Aug 2020 10:00:50 -0700, wrote:

Thanks for all the great info Jeff. This surveying I want to do is
not for legal reasons, mainly to just make sure I know where some of
the property line probably is and where a corner marker should be.
I have seen the corner marker but it may now be under a fallen tree.
A big hemlock that tipped over, as they tend to do, and the marker is,
I think, under the root mass or under the trunk right where it is the
largest, next to the root mass.

In this area, as soon as the surveyors are done, the locals like to
move the markers to a location that favors their property. Two of my
neighbors were having a dispute over a lot line adjustment. They paid
a professional surveyor to survey the property. I was home at the
time and watched them work. I then photographed the location of all
the markers because two of them were one side of my property. Two
days later, the markers had all moved. I'll spare you the rest of the
fiasco. At one point, I used a smartphone and Mobile Topographer Free
to demonstrate that the markers had been moved, which mostly solved
the problem.

I do have one thing in my favor, and that is a monument at the end
of my road that marks one corner of my property. So I could do as you
say and check its location with my GPS. Then I will know how far off
my measurement is after doing as you suggest. But only at that one
place.

You need at least two benchmarks to establish a point. Even if you
use a GPS, you will still need to account for ground movement using
the markers. In 1989, we had an earthquake, which moved things.
https://www.conservation.ca.gov/cgs/earthquakes/loma-prieta
The Pacific plate moved 6.2 feet to the northwest and
4.3 feet upward over the North American plate during
Loma Prieta.
Land west of the fault has been moving to the northwest
relative to land on the east at an average rate of 2 inches
per year for millions of year.

Since the GPS satellites did NOT move during the earthquake, a 6 ft
error makes surveying a bit of a challenge. The local benchmarks were
installed when the area was first subdivided into vacation tent sites
in about 1926. That would be about a 320 ft discrepancy between the
current GPS location and the 1926 survey marker. I somewhat verified
this about 5 years ago when I found a 200 ft discrepancy, but have
never bothered to ask the county how they handle such things. Since
most everything on the ground moves together, my guess(tm) is that the
county uses the surveyed benchmarks, and NOT the GPS location.
Depending on the age of your monument, you may have the same problem.
Ask your county how they handle ground movement.

This might help
https://gis.santacruzcounty.us/DPWScans/recordmaps/100M39.pdf
It's a 2001 survey of the property across the road from my house. Note
the copious use of found markers on the map as the "basis for
bearings". My guess(tm) is that they're trying to reconcile their
positions with that of the original 1926 sub-division map:
https://gis.santacruzcounty.us/DPWScans/recordmaps/024M02.pdf
without ever referring to GPS derived positions. If true, that will
make using GPS locations rather difficult. You will need two or more
monuments or benchmarks to adjust the property marker locations. The
2001 survey above used 7 markers.

Good luck with the project.
Yeah, I didn't consider the monument moving. I live practically on top
of the South Whidbey Fault and there is motion associated with both
the fault and the whole region. The plate Whidbey is on is rotating
clockwise and just a few miles from me the island is moving a couple
millimeters per year.
Thanks Again,
Eric