At least here in the east ....water is the first place folks would throw it. Check near the river. Also they would throw trash where they couldnt plant and far enough away from the house as to not invite critters.
Consistent with what many others have said, look in ditches, gullies, ravines, creeks, etc. they dumped there to help reduce erosion. But then a big rain might come along and wash some stuff on further down.
I would hit the purple stuff, but it looks like the new road bridge took out a corner of the wall, which could have been a good spot. This would apply if the house was on a knoll, good luck.[]
I was in the weedy field behind the house foundation today cleaning up 1980s litter so I would not damage my ATV tires and I was pulling up a modern beer bottle and then what comes up with it but an 1890S DEMIJOHN SHARD AND A PIECE OF AN 1858 MASON JAR!!!! AAAAA!!!!!!!!!!!!!!! And not to mention a whole sickle bar mower buried in the grass and crock shards!
If the grass is so deep as to hide a mower, there could be a lot of broken glass there, too. Tread carefully. I'd probably try raking back as much grass as possible to see what lies beneath. Sounds like a good lead to me.