"The first trial of a plutonium implosion weapon, the explosion on the ground produced radioactive fallout contaminating over 1,100 square miles of the state, although some debris spread as far north as Canada," the archive said in a statement on the documents.
The documents were published on the 79th anniversary of the first nuclear weapon test on July 16, 1945.
Six weeks after the test, there was a "swath of fairly high radioactivity" on the ground covering an area of approximately 100 miles long by 30 miles wide, a Los Alamos Laboratory report said.
Newly released materials also reveal that the US prepared for possible evacuations, fallout monitoring and the eventual discovery of nearby people that were exposed to potentially hazardous levels of contamination, the archive said.
The biological and public health impact of low-level radiation remains a contested issue, the archive said.
However, researchers at the National Cancer Institute have concluded that the test’s fallout contributed to an excess number of thyroid cancer cases, the archive added.