1. (On June 6, 1897), they traveled (across the Golden Gate Bridge).

2. They have been producing vegetables and cotton (for many years).

3. (During most seasons), the crops grow well (in this central valley).

Tell what each adverb phrase in () modifies.

1. On June 6, 1897--traveled
across the Golden Gate Bridge--traveled

2.for many years---have been producing

3. during most season--grow
in this central valley--grow

Looks good. But I think "in this central valley" modifies "well."