What source would be best for finding out what exact year it was in the 1870s when wheat was most productive or when rainfall was highest

What do you mean determine? answer in comment section.

Driven by a goal, duty, or curiosityhas a relatable character flawloyal to cause, family, and alliesexperiences changebrave and courageoussuperior intelligence or strengthinvokes trust or likeability

Don’t use this i just need to answer a question to ask one.