According to the passage a mound is a

A mound is a heaped pile of earth, gravel, sand, rocks, or debris.

Explanation:

The inference reader can make about the public’s reaction to the first Indy 500 Festival Parade is, The public approved of the parade.

Explanation:

The Indy 500 Festival Parade is a parade which takes place in the streets of Indianapolis, and this parade is marked as nation’s largest parade which takes place every year.

If we talk about the public’s reaction on the first 500 Indy Parade, we can draw the inference (conclusion) that the parade is very much approved by the Public. The line from the passage, ‘Now, every year, cheering fans line the parade route to watch this annual event’ indicates people’s interest and love for the parade.