In 1936, John Steinbeck toured the migrant camps and government camps of California. He wrote seven articles about the plight of the migrant workers that were published in The San Francisco News. The Harvest Gypsies is the compilation of those articles.
Having read The Grapes of Wrath there's not much to say about The Harvest Gypsies. It's clear Steinbeck was greatly moved by his experience in 1936, and it was this series of encounters that was the catalyst for his 1938 Pulitzer-winning novel. Elements of many of the stories Steinbeck tells in The Grapes of Wrath are first seen here. Told in a concise, largely journalistic voice, The Harvest Gypsies doesn't leave too much room for the Steinbeck we love, but he does make brief appearances.
The Harvest Gypsies is a very thin book primarily for Steinbeck fans. It also serves as a great companion to The Grapes of Wrath. It's not one I'd recommend to readers who have not read and loved The Grapes of Wrath.