There are a total of 12 anomalies available in the game, and they appear as a small formation of rocks that can be tuned into using the radio. Some of them are found behind locked doors, so it is advised that you wait until you unlock the new radio before going for all the collectibles. While going for anomalies, you should also go for Maggie Adler's Letters in order to unlock:
A video guide showing
all 25 collectibles available in Oxenfree can be found below:
0:12 - Maggie Adler Letter #13 - Main Street
0:54 - Maggie Adler Letter #4 - Main Street
1:20 - 105.1 Anomaly - Epiphany Field
1:44 - Maggie Adler Letter #1 - Epiphany Field
1:58 - Open Estate Gate
2:02 - 100.3 Anomaly - Discovery Cliffs
2:29 - Maggie Adler Letter #6 - Discovery Cliffs
2:42 - Maggie Adler Letter #12 - Beacon Beach
2:56 - 102.3 Anomaly - Epiphany Field
3:36 - Maggie Adler Letter #3 - Harden Tower
4:04 - Maggie Adler Letter #11 - Towhee Woods
4:41 - 103.5 Anomaly - Towhee Woods
5:26 - 99.9 Anomaly - Bridge Stand
5:57 - Maggie Adler Letter #8 - Bridge Stand
6:05 - 101.1 Anomaly - Bridge Stand
6:45 - 91.5 Anomaly - Camp Grounds
7:21 - Maggie Adler Letter #9 - Camp Grounds
7:44 - 97.9 Anomaly - Camp Grounds
8:28 - 106.7 Anomaly - Relay Point
8:56 - Maggie Adler Letter #10 - Relay Point
9:09 - 89.9 Anomaly - Facilities
9:40 - Maggie Adler Letter #5 - Facilities
9:56 - 94.3 Anomaly - US Army RCS
10:23 - Maggie Adler Letter #7 - US Army RCS
10:31 - 104.7 Anomaly - Milner Outpost
10:47 - Maggie Adler Letter #2 - Milner Outpost