The story made headlines previously after it was reported that Armstrong's girlfriend, Anna Hansen, originally took responsibility for the December 28 collisions. Hansen later admitted that she lied to avoid media attention.
As part of a plea agreement with prosecutors, Armstrong entered his plea by mail on Friday, according to USA Today, which reported that Armstrong paid $238.50 to cover court fees and a $150 fine.
Deputy District Attorney Andrea Bryan told the newspaper that it is common for people enter pleas by mail in such cases. Careless driving can be punished by up to 90 days in jail, but Bryan told USA Today that jail time is rare.
It was a rough week in the courts for Armstrong, who on Monday was ordered to pay $10 million to SCA Promotions, the Texas firm that underwrote a $5 million bonus awarded after his 2004 Tour de France victory. The company spent two years fighting against paying the bonus after the first allegations of Armstrong's doping appeared in the book L.A. Confidentiel by David Walsh and Pierre Ballaster. SCA Promotions settled out of court in 2006 after a lengthy arbitration, paying the original $5 million bonus plus $2.5 million in court costs.
In 2012, Armstrong was handed a lifetime ban from the sport and stripped of those seven Tour de France titles for doping. When Armstrong confessed to doping in 2013, the company began working to revisit the legal case. Last February, a judge cleared the way for SCA Promotions to reopen the lawsuit.
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Valverde disappointed with second in Oman
Mixed bag for MTN-Qhubeka during Andalucia's first day
The first day of racing at Vuelta a Andalucia proved to be mixed bag for MTN-Qhubeka, which had five riders riders go down in crashes during the morning road race before Tyler Farrar finished fifth.
"The morning stage was really easy until about 25km to go when the crosswinds started to come into play," said MTN's Jay Thomson.
"With no team really committed to making it split and everyone still having fresh legs, it was destined to be crazy in the final. Steve, Matt and myself were right in front to set up Tyler for the sprint but an AG2R rider touched wheels and took out 3 of us among the 30 odd other guys in the bunch."
Team director Alex Sans Vega said the trouble started with about 7km to go.
"Four Alpecin and two Sky riders went down right at the front of the bunch because of the crosswinds and high speed," he said. "With 5km to go there was yet another big crash that split the bunch further. Matt, Jay, Songezo, Merhawi and Nic all hit the deck. Fortunately none sustained any major injuries. After the crashes the race was so disorganised at the front but Tyler managed to get through the chaos and finish 5th."
The African squad regrouped for the technical afternoon time trial and finished in one piece. Steve Cummings finished 28 seconds behind winner Javier Moreno (Movistar ) to place 32nd.
The race continues Thursday with a 194km road stage.
