Fahrenheit 451 has been published numerous times over the years so the page numbers are going to be somewhat different depending on which edition you are reading. I am using the 2003 Del Ray edition which describes the destroyed city in the final ten pages of the book. Remember that a simile is a type of metaphor that compares two different things using like or as.
On page 160, as the bombs strike the city, everything is thrown violently into the air. The narrator describes how everything in the city is displaced by the explosions. For an instant, the city is blown into the air where it seemed to be "a mural hung like a reversed avalanche...." Here, a simile is used to compare what the city looked like at the moment of its destruction to the improbable sight of an upside-down avalanche.
On page 162, there is another comparison, though the inclusion of the word "looks" means that this is technically not a simile (because it is not directly comparing unlike things). Granger has just taken his first look at the rubble that once was the city, and he remarks to Montag that it "looks like a heap of baking powder." Very few of us have actually seen a flattened city. Yet, we can all imagine what a pile of baking powder looks like. This statement helps both the characters and the readers make sense of the total destruction of the city.