Any home info such as age, location, number of owners might help.

tj

The steel rims are probably the remains of some sort of pipe structure. The fact that they are 20' apart and "identical" would indicate they were built for the same purpose.

Does it seem logical that this was the remains of a large advertising sign, that could be seen from a freeway? Some sort of shopping center or other large store or distribution warehouse?

Are you close to a current or previous airport so that it may be some sort of navigation device?

From the picture the size of the pipe looks to weak for an overhead crane or similar device.

Download Google Earth, locate your home, then use the Historical Imagery slider to see if there's any image of what was there:
https://sites.google.com/a/earthoutreach.org/newreleases/outreach-announcements/ge5/tutorial-historical-imagery

Another possible use for the slabs would be a cloths line. A cloths line was used to dry cloths before the electric cloths dryer. My mothers was between to T shaped pipe poles about 25' a part. The poles were set in concrete.

Google earth is an excellent suggestion. With the click of and icon you can look at historical maps by moving the sliders. If you have not download google earth to your computer you are missing so much.

;You can also see street views of most places in the US, The measurement tools are excellent. You can measure straight line distances, you an measure a path between two points, and using the polygon tool you can measure the area of any polygon you can draw. The polygons can be the size of a state, the size of a drainage area, or the size of your lot.

I am sorry about the confusion in the original post. I don't know if it is my browser or some thing new in the forum's compose windows but periodically messages get messed up

How far apart are the two slabs?

Is the metal rim on the two holes threaded (like to screw something into)?

I'm inclined to suspect foundation for a clothes line, too. The 1954 addition to my 1904 home had posts for a clothes line, but they were individually set in concrete, as you would do for metal fence posts. They were nasty heavy suckers to remove!

Cement slabs for clothes lines would be overkill. A set of iron monkey bars maybe but not a clothes line. Knowing how far apart the holes within each slab are and their depth might help as well as its orientation with respect to the house. We need more info.

tj