The characteristic of the granite intrusion that provides the most evidence that it solidified deep underground is the presence of large, interlocking crystals.

Here's why:

* Slow Cooling: Granite forms from magma that cools and crystallizes very slowly. This slow cooling process allows for the formation of large, well-defined crystals.

* Depth and Pressure: The immense pressure deep underground prevents rapid cooling. This slow cooling rate is crucial for the formation of large crystals.

* Absence of Vesicles: Granite intrusions typically lack vesicles (gas bubbles) that are common in volcanic rocks. This absence further suggests that the magma cooled slowly and deeply, where the pressure was high enough to prevent gas expansion.

In contrast, extrusive igneous rocks (formed on the surface) like basalt have smaller crystals because they cool quickly.

So, the presence of large, interlocking crystals in a granite intrusion is a strong indication that it solidified deep within the Earth's crust.