Kern County (highly dependent on Delta water) generates about 20% more agricultural revenue than the 5 Delta Counties combined. However, there are 4 times more farm proprietors in the 5 Delta Counties than Kern (about 9,000 vs 2,250 according to BEA which is based on tax returns).
Comparing Kern County to San Joaquin County (by far the biggest Delta ag county) in the 2007 Census of Agriculture reveals that Kern County has 2,117 farms that average 1,116 acres. In contrast, San Joaquin County has 3,624 farms that average 204 acres. Ag receipts in Kern are about $4 billion a year, roughly double the $2 billion in San Joaquin. Kern County has nearly 3 times as many agricultural employees than San Joaquin County (45,000 vs 15,000), but about half the number of farm proprietors.
Although their rhetoric is over the top, it does show that there is some truth behind Delta partisans portrayal of themselves as small family farms versus big "corporate" farms.
Update: I eliminated some criticism of a recent PPIC report from this post. It had some miscalculations and was stronger than warranted, and distracted from the main point above.