Another week, another big animal rescue operation led by the Humane Society of the United States.

This time, it was a puppy mill in Kennewick, Washington where nearly 400 dogs were living in plywood boxes, chicken wire cages and shopping carts.

It was a case, described by Benton County Sheriff Larry Taylor, of "heartbreaking cruelty."

Fifty members of HSUS's Animal Rescue Team removed 369 American Eskimo dogs and puppies from deplorable conditions in what may be the largest puppy mill case in Washington history.

Here's how Scotlund Haisley, senior director of Animal Services for HSUS, described what rescuers found:

As our team of fifty strong fanned out across the property, we witnessed unspeakable cruelty: dozens of dogs crammed on top of one another in home-made chicken wire cells, rusty pens caked with feces, makeshift cages created with plywood and rusty metal doors. As I neared two shopping carts I saw something that I could only hope wasn't real---two dogs confined inside and wooden planks tied across the tops in their make-shift crates. These two dogs barely had enough room to turn around. I was later told that these dogs had lived their entire lives—which could be upwards of twenty years-- in those carts. We were overcome with emotion as we pried away the wooden bars and freed these two elderly dogs. After living in isolation and intensive confinement, their unexpectedly calm demeanor surprised me. It was as if they knew we were there to end their years of suffering.

The two dogs rescued from their shopping cart cells have joined more than 370 others now under the care of UAN, HEART, and HSUS at our emergency shelter. At the end of a very long day we received the ultimate good news —the owner surrendered all of the dogs and they are now in the custody of The HSUS.

There were several pregnant dogs, two nursing moms with babies and  - as a local humane staff member put it - "a female so old that her teeth are rotting and who shakes uncontrollable from a life of pregnancy, labor and confinement," according to the Tri-City Herald.

The owner, Ella Stewart who had operated the kennel since 1967, faces animal cruelty charges.

Washington is among the states that recently approved legislation aimed at cracking down on puppy mills. The new law, which takes effect Jan. 1, 2010,  puts a cap on the number of dogs kennels can keep and establishes basic animal welfare standards.