Rio del Lago 100 Mile Race Guide
The Rio del Lago 100 is an out-and-back hundred-mile trail race around Folsom Lake in Northern California. The event begins and ends at Beal’s Point in the Folsom Lake State Recreation Area, taking runners south along the American River Parkway to historic Auburn before returning on the same trails. Although much of the course overlaps legendary events such as the American River 50 and Way Too Cool 50K, the full loop covers 100 miles with one point where runners retrace their steps, creating an out-and-back format that includes a small return loop at the lake’s far end. You will encounter a combination of gentle shoreline running, rolling foothills and a series of climbs concentrated in the midsection. The finish line awaits back at Beal’s Point, where runners complete 100.5 miles of memorable terrain.
When It Is Run
Each year Rio del Lago takes place in early November, typically on the Saturday when Daylight Savings Time ends. For 2025, the start time is 6:00 AM on November 1, with runners racing through the night and into the following morning. The race calendar is designed to coincide with cooler fall temperatures in the Sierra Nevada foothills, and the daylight savings shift means the race begins before the clocks fall back. Temperatures can range from crisp pre-dawn chill around 40°F at the start to daytime highs near 60°F, then dip again overnight. Weather can be unpredictable, so runners should prepare for clear skies, possible wind off the lake, and the chance of rain.
How to Qualify or Register
Registration opens online via UltraSignup and is first-come, first-served for a field limited to 150 participants. Entry typically becomes available in mid-December and fills rapidly; all fees are non-refundable and non-transferable. Each entrant must be at least 18 years old and provide proof of previous ultramarathon experience, as the race serves as a Western States 100 qualifier. Runners receive B-tag timing chips, three on-course drop bags, and must carry their own cup and hydration system. Packet pickup is held the day before the race at the local Fleet Feet store in Folsom, where mandatory equipment and B-tag instructions are distributed. Crew access is allowed at designated aid stations, but some locations prohibit crew support, so study the course guide carefully.
Particular Challenges
While the overall elevation gain is moderate compared with some 100-mile races, the midsection contains three steep climbs of approximately 800–900 feet each within miles 40–74, condensed into a short span that can fatigue legs after an initial paved loop. Running the first 19 miles on smooth bike path and pavement can tempt competitors to start too fast, leading to early glycogen depletion and muscle soreness when the single-track climbs begin. Nighttime navigation under headlamps on forested trails poses its own challenges, and temperatures can drop below freezing before dawn. The remoteness of some aid stations means that if you miss one cutoff, there may be a long, dark stretch before the next. Mental endurance becomes the principal test as the course length and night hours accumulate.
Elevation Profile
Runners face 14,117 feet of total ascent and the same descent, starting at about 485 feet above sea level and reaching a maximum of 1,577 feet on the Nimbus Bluffs. After the gentle first 18 miles, the course climbs sharply from mile 40 to 43 (800 ft), again from mile 52.5 to 57.5 (900 ft), and a final 800-ft push between miles 69 and 73. The steepest grade (approximately 350 feet gain in one mile) occurs on the ascent out of the Lake Natoma Loop. Each climb is followed by fast runnable descents, but the concentration of vertical gain in the middle third means runners may hit “the wall” as they try to maintain pace in the dark.
Terrain Breakdown
Nearly the entire 100 miles is on unpaved trails (95%), including single-track paths and fire roads that reward hikers’ poles and careful footing over roots, rocks, and occasional muddy sections. The remaining 5% is paved bike path around Folsom Lake and connecting sections of the American River Parkway. You will experience smooth asphalt for the first 18 miles, then alternating trail surfaces—packed dirt, loose gravel and occasional creek crossings—throughout the remainder of the course. Some creek fords and boardwalk sections require caution after rains, and fire roads can be prone to washboarding in dry conditions.
Time Limit & Cutoffs
Competitors must finish within 30 hours, with departure cutoffs strictly enforced at each of the 17 aid stations. The first major loop (miles 0–18.7) has a cutoff around 6 PM, ensuring runners remain on pace to complete by the 30-hour mark. Thereafter, each station enforces a leave-by time aligned to a sliding pace chart respectful of night-time slower running. Missing any cutoff results in disqualification, so it is vital to monitor splits and aid-station departure times. The final absolute cutoff at Beal’s Point is typically around 11:00 AM the next morning; runners beyond that time are pulled for safety. Always consult the official pace chart provided at packet pickup for exact station times and distances.
Aid Stations
Rio del Lago 100 features fifteen aid stations spaced roughly every four to ten miles, with the closest stations under three miles apart in the mid-course hill section and longer stretches of eight to ten miles around the lake shore. Crews may access designated stops including Beal’s Point, Beal’s Point Medical Check, Granite Beach, Rattlesnake Bar, Overlook, Cool Fire Station, and the final Beal’s Point finish area. Three official drop‐bag locations are provided at Rattlesnake Bar, Overlook, and Auburn Lakes Trail, allowing runners to swap shoes, lights, or clothing. Medical checks occur at Beal’s Point medical, Rattlesnake Bar medical, Overlook medical, Auburn Lakes medical, and the final Medical Check before the finish. Pacer pickup is only allowed after 47.3 miles at Cool Fire Station and again after 54.6 miles at Overlook, ensuring solo effort through the early miles.
Mandatory Gear
All runners must carry a timing B-tag and personal cup or hydration vessel for cold or hot drinks, as cups are not provided on course. A headlamp with spare batteries is strongly recommended for overnight sections, and reflective gear or a vest improves visibility on multi‐use bike paths. Entrants must carry adequate water capacity to handle the longest water‐only section between Cardiac water‐only and adjacent aid stations. Trail shoes with sufficient tread for rocky single‐track are advised, though road shoes may suffice on smoother sections. Emergency blanket, whistle, and basic first‐aid kit are recommended items for safety in remote segments.
Crew & Pacing
Crew support is welcomed at allowed aid stations but prohibited at “no crew” stops such as Negro Bar and No Hands Bridge, with any violation resulting in disqualification. Pacers are permitted only after the Cool Fire Station (mile 69.45) and Overlook (mile 76.85) until the finish. Vehicle access to crew at aid stations requires State Parks parking passes; crews must pay for parking at the Folsom Lake Recreation Area while runners receive one pass for overnight parking at Beal’s Point. Course roads are closed to private traffic beyond aid station parking, so crews must plan finish‐area logistics accordingly.
Navigation
The course is marked continuously with orange trail tape that has reflective ends for night visibility, supplemented by painted arrows on pavement segments and wooden directional signs at junctions. Runners are advised to download the official GPX file and carry a GPS device or smartphone loaded with the track. Pre-race briefings highlight sections where private landowners occasionally remove ribbons, so familiarity with the course narrative, available on the event website, is crucial. In the rare event of confusion, cell coverage is generally good except near Rattlesnake Bar and Auburn Lakes Trail, where network service may be spotty.
Finish Rates
Historically, Rio del Lago 100 draws 150 starters with approximately 120 finishers, yielding an average completion rate near 80 percent under the 30-hour time limit. Faster climbers targeting sub-24-hour finishes often enjoy a 90 percent success rate, while back-of-the‐pack runners face greater risk of missing cutoffs during the remote nighttime miles. Factors such as early pacing on flat first loops and concentrated mid‐course climbs influence finish rates year to year, but overall the well-stocked aid stations and clear marking support strong completion statistics.
Special Features
Rio del Lago serves as the final Western States 100 qualifying race each year, granting coveted UTMB Index points and lottery qualification slots. All finishers earn a commemorative medallion, while those finishing under 30 hours receive a custom‐engraved belt buckle. The race shirt, lightweight pull-over, and finisher’s athleisure gear celebrate the scenic Folsom Lake backdrop. Unique awards include fastest first-time 100-mile finisher and oldest finisher recognitions, honoring milestones that highlight the diversity of the ultra community.
Previous Winners
In 2024, Greg Miller claimed the men’s title in 17:22:35, while Rachel Entrekin led the women in 19:16:06 on a crisp November day. Past champions include top Western States qualifiers and veteran ultrarunners who leverage Rio’s runnable shores and challenging Meat Grinder climbs to clock fast times during the early fall season. Each year’s podium often features a mix of local California trail specialists and out-of-state athletes testing their early-season fitness on the course.
Official Contact Info
For detailed race information, registration updates, and volunteer inquiries, visit the official Rio del Lago website at rio100mile.com or email the Race Director at info@rio100mile.com. Packet pickup details and parking instructions can be found under the “Runner Resources” section, with phone support available through the NorCalUltras office at (916) 765-6021.