Nonpareil, as the premier nut, is predominate. The necessary cross-pollinating varieties alternate rows. They all bloom with close timing. The Nonpareil is first. Fritz is an excellent pollenizer for Nonpareil, blooming with or just after the Nonpareil. Butte and Monterey pollinate the late Nonpareil bloom.
Observe this map diagram. It depicts the variety by row number. Note that the rows are numbered starting from the North working South. Also, notice that the varieties carry through from West Field into the East Field. This streamlines the mechanics of planting, harvest and post harvest sanitation. After tree shake the fallen nuts are processed independently however. West field yield is shipped/processed separately from that of the East field. One can visualize how the varieties are organized. The red path lines denote Nonpareil. Green for Butte. Yellow is Fritz and Blue is the Monterey.
An expert might know the difference but Almond trees all look the same to the layperson. There are [somewhat faded] marking letters brush painted on the tree trunks at the row ends. (e.g. N signifying Nonpareil) to assist. This map reference is the more durable record. Confusing a variety would be a blunder.
The Monterey planting is a bit of mystery. It is said that the layout was conceived without adequate planning notice given to the tree nursery supplier. We are unsure which was unavailable. The Monterey or the Butte variety.