Ubuntu – Unable to run salt.highstate

I'm working on configuring a group of 40 servers to be managed by SaltStack. I'm testing with just one minion at the moment, which I have successfully added to the master. For simplicity, I'm using the latest version of salt and salt-minion from the Ubuntu 14.04.1 package repository on the respective machines.

I have what appears to be a sane configuration and directory structure, however whenever I try running salt '*' state.highstate, I get an error that the top file does not match the nodes. If I try manually running a state file with salt '*' state.sls worker.users, it errors that no such file exists. Directory structure and files are below.

Any idea why this is not working?

root@salt-master:/srv/salt# tree /srv/salt
/srv/salt
├── worker
│   └── users.sls
└── top.sls

1 directory, 4 files

root@master:/srv/salt# salt '*' state.highstate
worker-2:
----------
    State: - no
    Name:      states
    Function:  None
        Result:    False
        Comment:   No Top file or external nodes data matches found
        Changes:

Summary
------------
Succeeded: 0
Failed:    1
------------
Total:     1

The contents of the relevant files:

root@master:/srv/salt# cat top.sls
base:
  '*':
    - worker.users
root@master:/srv/salt# cat worker/users.sls
    worker:
      user.present:
        - fullname: Service Account
        - shell: /bin/bash
        - home: /home/worker

    admin:
      user.present:
        - fullname: Search Admin Account
        - shell: /bin/bash
        - home: /home/admin

File root is defined as follows in the master and I've restarted all the machines:

file_roots:
  base:
    - /srv/salt