Final answer:
The canyon is vulnerable to erosion and landslides due to lost vegetation and predicted rain; mitigation involves access restrictions and education. The Acasta Gneiss's age is determined by radiometric dating; it's a rare metamorphic rock that is exposed through geological processes and is older than oceanic crust due to differing crustal recycling mechanisms.
Step-by-step explanation:
The canyon and recreation area mentioned are likely to experience several geological and hydrological hazards given the surrounding conditions. With the loss of significant vegetation due to wildfires, the soil stability is compromised, making the area vulnerable to erosion and landslides, especially with the predicted monsoon rains. The steep slopes further exacerbate the risk. To mitigate these risks and ensure public safety, the Forest Service could implement restrictions on access during high-risk periods, invest in early warning systems, create buffer zones with controlled vegetation growth, and educate the public on the hazards.
As for the museum tour guide question, scientists determine the age of rocks like the Acasta Gneiss through radiometric dating techniques which measure the decay of isotopes within the minerals. 'Gneiss' refers to a type of high-grade metamorphic rock known for its alternating bands of different minerals. It's rare on Earth's surface because most gneiss forms deep within the continental crust and requires significant geological processes to uplift and expose it. Continental rocks are generally older than oceanic rocks because continental crust isn't recycled through plate tectonics as oceanic crust is.