Can you please explain the structure of this sentence for me?

Hello, everyone. I was reading a quick story in order to improve my English. But when I read to this point of the story. I could not understand why and how did they use such a kind of the following sentence and it is not familiar to me ever as well?
White Fang watched some of the canoes go down the river.
I think the story tell us an event that happens in past. So all the verb should be in past.
So in the above sentence, I think “go” should be “went”
Then the sentence can be rewriten:
White Fang watched some of the canoes (that) went down the river.

The sentence cited from the book “White Fang”, author: Jack London, Oxfoxd University press, ISBN 0-19-424380-X, Series number: 9 780194 243803

Many thanks.

[size=150]White Fang watched some of the canoes go down the river.[/size]

[color=green][i]The word “go” in the sentence is an infinitive such as “to go”.
That’s why it was used in the basic form “to go” and not “to went”.
However, the word “to” is omitted when the infinitive is used after certain verbs such as make, see, hear, watch, let or made, saw, heard and watched etc. . . .
In such case it is called “ infinitive without to ”.

e.g.
He made her cry.
I saw you go.
You heard him sing.
She watched him play.
etc.

Hope this help !

Nick[/i]

I’ve read the novel by Jack London but I don’t remember whether White Fang

was watching some of the canoes while they were going down the river. or
was watching some of the canoes that/which were going down the river. or
was watching some of the canoes going down the river. or
watched some of the canoes going down the river. or simply or
watched canoes going down the river or even
watched canoes go down the river.

I am also not sure do grammarians say that the verb to go took the present subjunctive form here in the last variant.

Thanks