Well,

in general that depends a lot on ground water and oxygen.

Metals will corrode to the oxides, that would need not more

than some hundred years even for the most bulky objects of

aluminium.

Glas:

is leached slowly in water, eg the acheologists have a

"obsidian clock". Obsidian (volcanic glas) often used in

precolumbian cultures, buried in wet soil will show thin

layers of leaching process, one layer per year,

similar to growth rings of trees.

The leaching depends very much on the composition

of the glas, in general the alkalis and CaO is dissolved

some silicate-rich reisdue is left behind.

Such leached surfaces can look like an oil film on water.

But: if there is low or no streaming water, the glas will

last for millions of years. Think od the green glas

found in the desert in western egypt. (from a comet impact)

Georg

LANDFILL HUMAN CONTENTS (CEMETARY) AFTER A FEW CENTURIES.

Slightly off subject but amusingly, it is predicted that breast enhancement devices (boob job bags) should last longer than bones in some soil types. That could cause bewilderment for future archeologist when they find teeth, fillings and boob job bags geometrically laid out.

Boob job bags have already been found to be useful forensically because they each have a unique serial number aiding in the identification of corpses.

In the "good" old days of

cold war, there was a joke about future archaeologists theories:

They will discerne  a region of "coca cola"-culture from 

a region of "non-coca cola", interpreting the glass waste.

Georg

I recommend reading  

''The world without us'' by Alan Weisman 2007.

Among other fascinating stuff he analyses how long various objects survive without human maintenance. I think he says that copper would remain recognisable the longest, possibly indefinitely.

There is even a website with some cool animations.