Upon us meaning

The preposition upon is generally much more formal than on but can be used to replace it in certain situations.

It can be used instead of on after several common verbs, such as happen, depend, insist and congratulate.

Examples are ‘He insistedupon seeing you even though I told him you were busy’, ‘A police patrol happened upon the robbers as they were running out of the bank’ and  ‘My whole future dependedupon the decision of one manager’.

Upon is also used to mean ‘immediately after’, as in ‘Upon his release from prison, Davis went immediately to his mother’s house’.

It can also mean ‘happening soon’ and in this case it is not normally replaceable with on, as in ‘Christmas is almost upon us again’ and ‘It’s June already and the exams will soon be upon us’.

When used between two nouns that are the same, upon emphasizes the large number or amount of the thing that has been mentioned, as in ‘I’ve written to you year upon year but I have never received a reply’ and ‘They drove for days across mile upon mile of open desert’.

Upon is also

is on a verb or adjective

is on a verb preposition or adverb