One in three American Indian women have been raped or have experienced an attempted rape, according to the Justice Department

Their rate of sexual assault is more than twice the national average. And no place, women's advocates say, is more dangerous than Alaska's isolated villages, where there are no roads in or out, and where people are further cut off by undependable telephone, electrical and Internet service. Native American women say that few, if any, female relatives or close friends have escaped sexual violence. "We should never have a woman come into the office saying, 'I need to learn more about Plan B for when my daughter gets raped,'" said Charon Asetoyer, a women's health advocate on the Yankton Sioux Reservation in South Dakota, referring to the morning-after pill. "That's what's so frightening - that it's more expected than unexpected. It has become a norm for young women." Women say the tribal police often discourage them from reporting sexual assaults. Reasons for the high rate of sexual assaults among American Indians are poorly understood, but explanations include a breakdown in the family structure, a lack of open discussion about sexual violence and alcohol abuse. Rape, according to American Indian women, has been distressingly common for generations, and they say that tribal officials and the federal and state authorities have done little to help halt it, leading to its being significantly under-reported. In the Navajo Nation, which encompasses parts of Arizona, New Mexico and Utah, 329 rape cases were reported in 2007 among a population of about 180,000. Five years later, there have been only 17 arrests. Women's advocates on the reservation say that only about 10% of sexual assaults are reported. Nationwide, an arrest is made in just 13% of the sexual assaults reported by American Indian women, according to the Justice Department, compared with 35% for black women and 32% for whites. In South Dakota, American Indians make up 10% of the population, but account for 40% of the victims of sexual assault. Alaska Natives are 15% of that state's population, but constitute 61% of its victims of sexual assault. The Justice Department did not prosecute 65% of the rape cases on Indian reservations in 2011. Despite the low rates of arrests and prosecutions, convicted sexual offenders are abundant on tribal lands. The Rosebud Sioux Reservation in South Dakota, with about 25,000 people, is home to 99 Class 3 sex offenders, those deemed most likely to commit sex crimes after their release from prison. The Tohono O'odham tribe's reservation in Arizona, where about 15,000 people live, has 184, according to the Justice Department. By comparison, Boston, with a population of 618,000, has 252 Class 3 offenders. Minneapolis, with a population of 383,000, has 101, according to the local police. In the Navajo Nation, Caroline Antone, 50, an advocate for the reservation's victims of sexual violence who has herself been raped, said that sexual assault was virtually routine in her community. "I know only a couple of people who have not been raped," she said. "Out of hundreds."